DOT/FRA/ORD-23/20 Final Report | July 2023

Locomotive Crash Energy Management 

Vehicle-to-Vehicle Tests 1 & 2: Analyses and 

Test Results 

i 

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1. REPORT DATE (DD-MM-YYYY)

9/9/2022

2. REPORT TYPE

Technical Report

3. DATES COVERED (From - To)

8/24/2018–5/10/2022

4. TITLE AND SUBTITLE

Locomotive Crash Energy Management Vehicle-to-Vehicle Tests 1 & 2: 

Analyses and Test Results

5a. CONTRACT NUMBER

6913G618F500083

5b. GRANT NUMBER

5c. PROGRAM ELEMENT NUMBER

6. AUTHOR(S)

Patricia Llana (ORCID 0000-0003-0885-4951) 

Dr. Richard Stringfellow* (ORCID 0000-0003-3730-0851) 

5d. PROJECT NUMBER

5e. TASK NUMBER

5f. WORK UNIT NUMBER

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

Volpe National Transportation Systems Center *CAMX Power LLC 

55 Broadway 35 Hartwell Avenue

Cambridge, MA 02142 Lexington, MA 02421

8. PERFORMING ORGANIZATION 

REPORT NUMBER 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

U.S. Department of Transportation 

Federal Railroad Administration

Office of Railroad Policy and Development

Office of Research, Development, and Technology 

Washington, DC 20590

10. SPONSOR/MONITOR'S ACRONYM(S)

FRA

11. SPONSOR/MONITOR'S REPORT 

NUMBER(S)

DOT/FRA/ORD-23/20

12. DISTRIBUTION/AVAILABILITY STATEMENT

This document is available to the public through the FRA eLibrary. 

13. SUPPLEMENTARY NOTES

COR: Patricia Llana (Volpe Center), Jeff Gordon (FRA)

14. ABSTRACT

Crash energy management (CEM) components which can be integrated into the end structure of a locomotive were 

developed: a push-back coupler and a deformable anti-climber. These components are designed to inhibit override and 

improve crashworthiness for equipped locomotives in a wide range of collisions. A full-scale dynamic impact test program 

has been designed to evaluate the CEM system. Two sets of coupling tests validated finite element models. Two CEM 

locomotive vehicle-to-vehicle collision tests and a train-to-train collision test are planned. This report describes the analyses 

and test results of both the first and second vehicle-to-vehicle impact tests.

15. SUBJECT TERMS

Locomotives, crashworthiness, railcars, couplers, crash energy management, push-back coupler, deformable anti-climber, 

override, collision, injury, impacts

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 

ABSTRACT

18. NUMBER 

OF

PAGES

118

19a. NAME OF RESPONSIBLE PERSON

a. REPORT Jeff Gordon

Unclassified

b. ABSTRACT

Unclassified

c. THIS PAGE

Unclassifie 

d 

19b. TELEPHONE NUMBER (Include area code)

617-494-2303
ii

METRIC/ENGLISH CONVERSION FACTORS

ENGLISH TO METRIC METRIC TO ENGLISH

LENGTH (APPROXIMATE) LENGTH (APPROXIMATE)

1 inch (in) = 2.5 centimeters (cm) 1 millimeter (mm) = 0.04 inch (in) 

1 foot (ft) = 30 centimeters (cm) 1 centimeter (cm) = 0.4 inch (in)

1 yard (yd) = 0.9 meter (m) 1 meter (m) = 3.3 feet (ft) 

1 mile (mi) = 1.6 kilometers (km) 1 meter (m) = 1.1 yards (yd) 

1 kilometer (km) = 0.6 mile (mi)

AREA (APPROXIMATE) AREA (APPROXIMATE)

1 square inch (sq in, in2) = 6.5 square centimeters (cm2) 1 square centimeter (cm2) = 0.16 square inch (sq in, in2) 

1 square foot (sq ft, ft2) = 0.09 square meter (m2) 1 square meter (m2) = 1.2 square yards (sq yd, yd2) 

1 square yard (sq yd, yd2) = 0.8 square meter (m2) 1 square kilometer (km2) = 0.4 square mile (sq mi, mi2) 

1 square mile (sq mi, mi2) = 2.6 square kilometers (km2) 10,000 square meters (m2) = 1 hectare (ha) = 2.5 acres 

1 acre = 0.4 hectare (he) = 4,000 square meters (m2)

MASS - WEIGHT (APPROXIMATE) MASS - WEIGHT (APPROXIMATE)

1 ounce (oz) = 28 grams (gm) 1 gram (gm) = 0.036 ounce (oz) 

1 pound (lb) = 0.45 kilogram (kg) 1 kilogram (kg) = 2.2 pounds (lb)

1 short ton = 2,000 pounds (lb) = 0.9 tonne (t) 1 tonne (t) =

=

1,000 kilograms (kg) 

1.1 short tons

VOLUME (APPROXIMATE) VOLUME (APPROXIMATE)

1 teaspoon (tsp) = 5 milliliters (ml) 1 milliliter (ml) = 0.03 fluid ounce (fl oz)

1 tablespoon (tbsp) = 15 milliliters (ml) 1 liter (l) = 2.1 pints (pt) 

1 fluid ounce (fl oz) = 30 milliliters (ml) 1 liter (l) = 1.06 quarts (qt)

1 cup (c) = 0.24 liter (l) 1 liter (l) = 0.26 gallon (gal) 

1 pint (pt) = 0.47 liter (l) 

1 quart (qt) = 0.96 liter (l) 

1 gallon (gal) = 3.8 liters (l) 

1 cubic foot (cu ft, ft3) = 0.03 cubic meter (m3) 1 cubic meter (m3) = 36 cubic feet (cu ft, ft3)

1 cubic yard (cu yd, yd3) = 0.76 cubic meter (m3) 1 cubic meter (m3) = 1.3 cubic yards (cu yd, yd3)

TEMPERATURE (EXACT) TEMPERATURE (EXACT)

[(x-32)(5/9)] °F = y °C [(9/5) y + 32] °C = x °F

QUICK INCH - CENTIMETER LENGTH CONVERSION

0 1 2 3 4 5

Inches

Centimeters 0 1 2 3 4 5 6 987 1110 1312

QUICK FAHRENHEIT - CELSIUS TEMPERATURE CONVERSIO

 -40° -22° -4° 14° 32° 50° 68° 86° 104° 122° 140° 158° 176° 194° 212°

 

°F

 °C -40° -30° -20° -10° 0° 10° 20° 30° 40° 50° 60° 70° 80° 90° 100°

For more exact and or other conversion factors, see NIST Miscellaneous Publication 286, Units of Weights and 

Measures. Price $2.50 SD Catalog No. C13 10286 Updated 6/17/98
iii

Acknowledgements

This work was performed as part of the Equipment Safety Research Program of the Federal 

Railroad Administration (FRA) Office of Research, Development, and Technology (RD&T). 

The authors appreciate the technical support and guidance provided by Jeff Gordon, Program 

Manager, RD&T. FRA staff at the Transportation Technology Center (TTC) in Pueblo, 

Colorado, helped coordinate efforts between FRA and Transportation Technology Center, Inc. 

(TTCI). The authors appreciate the technical support and efforts of both FRA staff and TTCI 

staff at TTC in conducting the equipment tests. The authors would also like to acknowledge 

Volpe National Transportation Systems Center colleague A. Benjamin Perlman for his ongoing 

technical advice and support in the research discussed in this report. 
iv

Contents

Executive Summary ........................................................................................................................ 1

1. Introduction ................................................................................................................. 3

1.1 Background ................................................................................................................. 3

1.2 Objectives .................................................................................................................... 4

1.3 Overall Approach ........................................................................................................ 5

1.4 Scope ........................................................................................................................... 5

1.5 Organization of the Report .......................................................................................... 5

2. Vehicle-to-Vehicle Test 1 Pre-Test Analysis .............................................................. 6

2.1 Pre-Test Finite Element Analysis ................................................................................ 6

2.2 Revised Pre-Test Analyses ........................................................................................ 12

3. Vehicle-to-Vehicle Test 1 Test Results ..................................................................... 15

3.1 Test Outcome ............................................................................................................ 15

3.2 Damage to the Equipment ......................................................................................... 22

4. Vehicle-Vehicle Test 1 Post-Test Evaluation ............................................................ 25

4.1 Data Review and Analysis ........................................................................................ 25

4.2 Comparison of Test Results with Pre-Test Model Predictions ................................. 33

4.3 Comparison of Test Results with Post-Test Model Predictions ................................ 38

4.4 Assessment of CEM Locomotive Damage/Repair Needs ......................................... 43

4.5 CEM Locomotive Repair .......................................................................................... 44

5. Vehicle-to-Vehicle Test 2 Pre-Test Analysis ............................................................ 46

5.1 Identification of Cab Car Test Vehicle ...................................................................... 46

5.2 Pre-Test Finite Element Analyses ............................................................................. 47

6. Vehicle-to-Vehicle Test 2 Test Results ..................................................................... 52

6.1 Test Outcome ............................................................................................................ 52

6.2 Damage to the Equipment ......................................................................................... 58

7. Vehicle-Vehicle Test 2 Post-Test Evaluation ............................................................ 67

7.1 Data Review and Analysis ........................................................................................ 67

7.2 Comparison of Test Results with Pre-Test Model Predictions ................................. 81

7.3 Assessment of CEM Locomotive Damage/Repair Needs ......................................... 90

7.4 Lessons Learned/Recommendations for the Train-to-Train Test .............................. 90

8. Construction of Finite Element Models .................................................................... 92

8.1 CEM Locomotive Coupler Carrier ............................................................................ 92

8.2 Conventional Locomotive Plow ................................................................................ 93

8.3 Modification of Collision Post and Other Short Hood Structures ............................. 94

8.4 Hopper Style Freight Car .......................................................................................... 95

8.5 CEM Locomotive Modifications ............................................................................... 96

8.6 Cab Car Modifications .............................................................................................. 98

8.7 New Coupler Models ............................................................................................... 100

9. Conclusion ............................................................................................................... 102
v 

10. References ............................................................................................................... 104
vi 

Illustrations

Figure 1. CEM locomotive comprising a DAC and PBC retrofit onto an F40 locomotive ............ 4

Figure 2. Schematic of CEM Vehicle-to-Vehicle Test 1 initial conditions .................................... 6

Figure 3. Side view of the model for a moving CEM locomotive (left) colliding with a 

conventional locomotive (right) .............................................................................................. 7

Figure 4. Detail showing colliding vehicle ends after 12.8” of crush; the coupler carrier bolts 

have failed ............................................................................................................................... 8

Figure 5. Detail showing colliding vehicle ends after 24.5” of crush; the shear bolts have now 

failed ....................................................................................................................................... 9

Figure 6. Detail showing colliding vehicle ends after 35” of crush (peak displacement) .............. 9

Figure 7. Deformation at 35” crush. Left — CEM locomotive; right — conventional locomotive

............................................................................................................................................... 10

Figure 8. Detail showing minimal deformation of conventional locomotive plow (red) at 35” 

crush due to impact with draft pocket side plates (blue) ...................................................... 10

Figure 9. Deformation of DAC at various extents of crush .......................................................... 11

Figure 10. Force-displacement curve showing contributions from PBC, DAC and other end 

structures ............................................................................................................................... 12

Figure 11. FE model calculated force-displacement curve at 21 mph collision for revised model 

using measured vehicle weights, with estimated contributions of key components ............. 13

Figure 12. FE model predicted vehicle speeds at 21 mph for revised model using measured 

vehicle weights ...................................................................................................................... 13

Figure 13. Comparison of revised FE model predicted force-displacement curves for collision 

speeds of 20 mph, 21 mph, and 22 mph ............................................................................... 14

Figure 14. Post-test photo of the locomotives .............................................................................. 15

Figure 15. Pre-test photograph of the coupler carrier ................................................................... 16

Figure 16. Post-test photograph showing the coupler carrier lying on the track .......................... 16

Figure 17. Pre-test photograph of the back of the PBC deformation tube .................................... 17

Figure 18. Post-test photograph showing the back of the PBC deformation tube ........................ 17

Figure 19. Deformed PBC deformation tube removed from the draft pocket; peeled paint has 

been removed ........................................................................................................................ 18

Figure 20. Damage to the limit stop mounted to the front of the sliding lug due to contact by the 

back of the PBC coupler head ............................................................................................... 18

Figure 21. Damage to rear of the PBC coupler head from limit stop contact............................... 19

Figure 22. Post-test photo of CEM system; close-up on the right ................................................ 20

Figure 23. Pre-test photograph of DAC ........................................................................................ 20
vii 

Figure 24. Post-test photograph of DAC showing that only the upper DAC tubes deformed ..... 21

Figure 25. Deformed upper DAC tubes, right and left sides, respectively ................................... 21

Figure 26. CEM locomotive damage ............................................................................................ 22

Figure 27. Conventional locomotive damage ............................................................................... 23

Figure 28. Close-up of conventional locomotive damage ............................................................ 23

Figure 29. Post-test photographs indicating lateral offset of the colliding vehicles ..................... 24

Figure 30. Left — carbody longitudinal accelerations (orange for stationary, blue for moving); 

right — strain at the top of the CEM coupler shank ............................................................. 25

Figure 31. Left — upper DAC deformations; right — carbody longitudinal accelerations ......... 26

Figure 32. Carbody longitudinal acceleration pulse drops to zero after about 0.175 second ....... 27

Figure 33. Successive integration of the acceleration pulses (top row) for the CEM locomotive 

(left) and conventional locomotive (right) yielded speed (middle row) and displacement 

(lower row) time-histories..................................................................................................... 27

Figure 34. Calculated vehicle speed time-histories ...................................................................... 28

Figure 35. Left — calculated relative vehicle displacement time-histories; right — schematic 

illustration of additional vehicle approach prior to force build-up after initial impact when 

couplers are open .................................................................................................................. 28

Figure 36. Top Left — a pre-test photograph of the couplers from above; bottom left — impact 

sensors affixed to the front surface of the stationary conventional locomotive; right — 

impact sensors affixed to the front surface of the CEM locomotive coupler ....................... 29

Figure 37. Upper left — vertical acceleration of carbody at CEM forward truck; lower left — 

integration of acceleration pulse to yield vertical speed (in mph); upper right — correction 

of speed curve to remove drift; lower right — integration of corrected speed curve to yield 

vertical displacement time-history ........................................................................................ 30

Figure 38. Force time-history based on single-degree-of-freedom approximation (F = ma) where 

‘m’ is the mass of the CEM locomotive and ‘a’ is the longitudinal acceleration at the center 

of the vehicle ......................................................................................................................... 31

Figure 39. Left — estimated time-histories of the force through the coupler based on data from 

strain gages positioned on the shank and near the pin; right — calculated averages forces for 

the three front (shank) and two rear (pin) gages overs the first 0.08 seconds after impact .. 31

Figure 40. Left — time-histories of strain behind the eight top and bottom shear bolts on the draft 

pocket side plates; right — time-histories of strain ahead of the eight top and bottom shear 

bolts on the sliding lug side plates ........................................................................................ 32

Figure 41. Left — comparison of measured displacement time-histories with model predictions; 

right — comparison of measured speed time-histories with model prediction .................... 34

Figure 42. Left — comparison of calculated test/model force crush curves (coupler only and 

total) ...................................................................................................................................... 35
viii

Figure 43. Left — contours of strain on the side of the draft pocket during deformation tube 

stroke ..................................................................................................................................... 37

Figure 44. Comparison of FE model prediction of CEM end frame mode of deformation with 

post-test photograph of the end frame (right) ....................................................................... 37

Figure 45. Comparison of revised FE model prediction of relative vehicle displacement with test 

results .................................................................................................................................... 39

Figure 46. Comparison of revised FE model prediction of vehicle speeds displacement with test 

results .................................................................................................................................... 39

Figure 47. Comparison of FE model prediction of force-vs.-crush with values calculated based 

on test results......................................................................................................................... 40

Figure 48. Comparison of predicted DAC deformation with test results ..................................... 41

Figure 49. Predicted deformation of conventional locomotive anti-climber apron and inner gusset 

plates ..................................................................................................................................... 42

Figure 50. Left — photograph showing cut-away left upper DAC tube and angled support plate; 

right — detail showing damage at top of connection between angled support plate and front 

plate ....................................................................................................................................... 43

Figure 51. Detail of deformed CEM locomotive at the end of the simulation of V2VT1 showing 

plastic deformation at the top of the welded connection of the angled support plate to the 

end plate, as indicated ........................................................................................................... 44

Figure 52. Left — outline of the bearing plate which will be welded to the front of the CEM 

locomotive end plate and onto which the angled gusset will be welded; right — illustration 

of the reinforcement gusset to be welded behind the end plate where the angled gusset plate 

was welded to the end plate .................................................................................................. 45

Figure 53. Schematic of CEM Vehicle-to-Vehicle Test 2 initial conditions ................................ 46

Figure 54. Buffer beam at forward end of M1 cab car selected for VTVT2 ................................ 47

Figure 55. FE model for CEM locomotive impact of a consist comprising a lead M1 cab car with 

two trailing hopper cars ........................................................................................................ 48

Figure 56. Predicted deformation after 0.25 seconds for a collision speed of 27.5 mph .............. 48

Figure 57. Predicted deformation after 0.25 seconds for a collision speed of 27.5 mph for model 

with flooring added back into the model, but only just past the forward door opening ....... 48

Figure 58. Predicted results for FE model with retrofit plywood flooring and coupler yaw 

rotation during impact at 29 mph collision speed: top — a side view showing all vehicles; 

bottom — a detailed side view showing the impacting CEM locomotive and cab car ........ 49

Figure 59. Predicted deformation at 28 mph collision speed: top — a side view showing all 

vehicles; bottom — a detailed side view showing the impacting CEM locomotive and cab 

car .......................................................................................................................................... 50

Figure 60. Predicted deformation at the target collision speed of 33 mph: Top — a side view 

showing all vehicles; bottom — a detailed side view showing the impacting CEM 

locomotive and cab car ......................................................................................................... 50
ix

Figure 61. Predicted force crush curve at the target speed of 33 mph and a breakdown of the key 

contributions to the total force, including the PBC, the DAC assembly, and deformation of 

colliding end structures ......................................................................................................... 51

Figure 62. Predicted deformation at the estimated upper limit of collision speed (35 mph): top — 

a side view showing all vehicles; bottom — a detailed side view showing the impacting 

CEM locomotive and cab car ................................................................................................ 51

Figure 63. Pre-test photo of the impact interface .......................................................................... 53

Figure 64. Post-test photo of the impact interface ........................................................................ 53

Figure 65. View of impacting couplers from below: M1 coupler on top, CEM loco coupler on 

bottom ................................................................................................................................... 54

Figure 66. DAC tubes after impact, before the vehicles were separated ...................................... 54

Figure 67. The deformed coupler carrier caught between the sliding lug and a bottom plate of the 

draft pocket ........................................................................................................................... 55

Figure 68. The view from inside the M1, looking at the CEM locomotive, before the vehicles 

were separated ....................................................................................................................... 56

Figure 69. The PBC deformation tube was expanded along its entire stroke of 21” .................... 56

Figure 70. Damage to the limit stop mounted to the front of the sliding lug due to contact by the 

back of the PBC coupler head ............................................................................................... 57

Figure 71. Sliding lug position before (left) and after (right) the impact ..................................... 58

Figure 72. Post-test impact vehicles: CEM locomotive (left), M1 cab car (right) ....................... 59

Figure 73. Upper and lower DAC tubes, post-test ........................................................................ 60

Figure 74. Post-impact deformation of bottom DAC tubes support plate, left (left) and right 

(right) sides ........................................................................................................................... 60

Figure 75. All shear bolts broke cleanly, except #5 (bottom row, second from right) ................. 61

Figure 76. Draft pocket deformed bolt hole.................................................................................. 61

Figure 77. One of the two sliding lug support plates was deformed ............................................ 62

Figure 78. CEM locomotive end plate deformation on left (left) and right (right) sides ............. 63

Figure 79. M1 coupler knuckle fracture (left), and a close-up of the fracture (right) .................. 64

Figure 80. Post-test damage to M1 end frame .............................................................................. 64

Figure 81. M1 draft sill before impact (top) and after impact (bottom) ....................................... 65

Figure 82. M1 carbody buckled inboard of rear doors ................................................................. 66

Figure 83. M1 interior damage, buckle at rear door ..................................................................... 66

Figure 84. CEM locomotive (left) and carbody underframe (right) center longitudinal 

accelerations (‘S’ for stationary, ‘M’ for moving) ................................................................ 67

Figure 85. Calculated vehicle speed time-histories ...................................................................... 68
x 

Figure 86. Vehicle relative displacement obtained from integration of the speed pulses shown in 

Figure 85 and subtraction of the respective vehicle displacement time-histories (left) and 

correction (right) ................................................................................................................... 68

Figure 87. Image from high-speed video annotated to indicate the distance just prior to impact 

between reference points on each vehicle. ............................................................................ 70

Figure 88. Image taken from a high-speed test video (approximately 280 msec after impact) .... 71

Figure 89. Still images from the overhead standing drone taken near the point of maximum crush 

(top) and after elastic rebound (bottom) ............................................................................... 72

Figure 90. CEM coupler longitudinal motion, as measured by string potentiometers DMCL_X 

and DMCR_X ....................................................................................................................... 73

Figure 91. Sliding lug longitudinal motion, as measured by string potentiometers DMSL_X and 

DMSR_X .............................................................................................................................. 73

Figure 92. DAC longitudinal motion, as measured by string potentiometers DMACR_X and 

DMACL_X (lower DAC tubes) DMACTR_X and DMACTL_X (upper DAC tubes) ....... 74

Figure 93. CEM forward (left) and rear (right) truck secondary suspension vertical displacements 

indicate less than 0.4” of body-to-truck relative displacement ............................................. 75

Figure 94. Cab car forward and rear truck secondary suspension vertical displacements ........... 76

Figure 95. Image captured from high-speed video approximately 480 msec after impact, showing 

the upward folding of the cab carbody at the induced buckle just forward of the rear doors, 

causing the rear truck wheels to lift off the rail .................................................................... 76

Figure 96. Force through impacting couplers estimated based on strain gage data and known 

coupler shank cross-sectional area ........................................................................................ 77

Figure 97. Colliding vehicle force-crush curve derived from CEM longitudinal acceleration data 

(Figure 84, left) and predicted relative displacement between the CEM locomotive and the 

cab car (Figure 86, right) presented for two filtering frequencies: CFC60 (standard) and 

CFC30 (non-standard) .......................................................................................................... 78

Figure 98. Left — time-histories of strain aft of the eight top and bottom shear bolts on the draft 

pocket side plates; right — time-histories of strain forward of the eight top and bottom shear 

bolts on the sliding lug side plates ........................................................................................ 79

Figure 99. Left — time-histories of strain near the top of the draft pocket side plates (‘1’ front 

and ‘2’ rear); right — time histories of strain along the web of the underframe main I-beams 

(‘T’ top and ‘B’ bottom) ....................................................................................................... 80

Figure 100. Comparison of predicted relative displacement vs. time curve with raw and corrected 

estimates obtained from test data .......................................................................................... 82

Figure 101. Comparison of force through the CEM coupler estimated based on coupler shank 

strain gage readings (see Figure 96, left) with FE model predictions .................................. 83

Figure 102. Comparison of total force vs. displacement derived from CEM longitudinal 

acceleration pulse with FE model predictions ...................................................................... 84

Figure 103. Contours of strain on the side of the draft pocket during deformation tube stroke ... 86
xi 

Figure 104. Contours of strain on the side of the draft pocket during deformation tube stroke ... 86

Figure 105. Comparison of FE model prediction of CEM end frame mode of deformation with a 

post-test photograph of the end frame (right) ....................................................................... 87

Figure 106. Comparison of FE model prediction (left) of cab car end frame mode of deformation 

with a post-test photograph of the end frame (right) ............................................................ 88

Figure 107. A graphic from the FE model showing the deformed cab, annotated with the 

undeformed distance from the back of the collision post to the middle of the forward of a 

pair of two windows.............................................................................................................. 89

Figure 108. Comparison of FE model prediction (left) of cab car draft sill mode of deformation 

with a post-test photograph of the draft sill (right) ............................................................... 89

Figure 109. Left — the front end of the modified CEM locomotive model, with the new 

representation of the coupler carrier highlighted in red; above right — the new coupler 

carrier model; below right: detailed side view of the modified CEM locomotive model .... 92

Figure 110. Front and back views of FE model for a conventional locomotive plow .................. 93

Figure 111. FE model of conventional locomotive with plow added ........................................... 94

Figure 112. FE model with hood removed to reveal collision post modifications ....................... 95

Figure 113. Side and isometric views of FE model of hopper-style freight car ........................... 96

Figure 114. Left — detail from FE model showing added stiffeners (red); right — size of bearing 

plate increased (larger rectangles highlighted in red) to include area where angled DAC 

supports were welded to front plate. ..................................................................................... 97

Figure 115. Excerpt from drawing 14424-0400 [8] showing that top DAC assembly extended 

18.875” forward from the end plate of the CEM locomotive ............................................... 97

Figure 116. Detail from modified CEM locomotive model showing 1.125”-deep sections added 

to the four DAC tubes and the angled support plates ........................................................... 98

Figure 117. Modified cab car FE model showing added flooring, highlighted in red .................. 99

Figure 118. Detail showing front end of modified cab car FE model with added buffer beam, 

highlighted in red, and small round discs representing the ends of springs coupling the 

buffer beam to the end beam of the car, highlighted in yellow ............................................ 99

Figure 119. FE model of cab car yoke ........................................................................................ 100

Figure 120. FE model of new cab car (28”, left) and CEM locomotive (31”, right) couplers ... 101
xii 

Tables

Table 1. Comparison of averaged measured peak strain levels (microstrain) during vehiclevehicle test with those from 9 mph coupling test; note that positive strain gage readings are 

compressive........................................................................................................................... 33

Table 2. Comparison of calculated energy absorption levels from the test with model predictions

............................................................................................................................................... 36

Table 3. Comparison of averaged measured peak strain levels (microstrain) during vehiclevehicle tests with those from 9-mph CEM coupling test[9]; note that positive strain gage 

readings were compressive ................................................................................................... 79

Table 4. Estimated timing of key collision events ........................................................................ 80

Table 5. Comparison of estimated CEM component energy absorption levels from the test with 

FE model predictions ............................................................................................................ 85
1 

Executive Summary

The Federal Railroad Administration (FRA), with support of the Volpe National Transportation 

Systems Center, is conducting research on the implementation of CEM features on locomotives. 

This report summarizes activities that supported full-scale vehicle-to-vehicle tests that evaluated 

two components retrofitted onto a conventional passenger locomotive to enhance its 

crashworthiness: a push-back coupler (PBC) and a deformable anti-climber (DAC). The 

modified locomotive design was based on the concepts generally referred to as “crash energy 

management,” (CEM) and thus has been termed a “CEM locomotive.” 

The work plan for the program called for four key activities: 

• Pre-test analysis for Vehicle-to-Vehicle Test 1 (V2VT1) — a collision between a moving 

CEM locomotive and a standing conventional locomotive 

• Post-test evaluation for V2VT1 

• Pre-test analysis for Vehicle-to-Vehicle Test 2 (V2VT2) — a collision between a moving 

CEM locomotive and a standing consist with a lead cab car and trailing freight car

• Post-test evaluation for V2VT2 

Researchers focused pre-test activities for both tests on developing and implementing finite 

element (FE) models that simulated the test collision and, in particular, helped determine the 

target speeds for the collisions. They chose the target speeds so that certain aspects of the CEM 

design could be assessed in the tests. Specifically, it was set at a speed that would cause 

complete exhaustion of the PBC system, failure of the shear bolts connecting the sliding lug to 

the side plates of the draft pocket, and crush of DAC elements to an extent that 50 percent of the 

required energy absorption capacity would be absorbed. Pre-test activities for both tests also 

included support of various aspects of test preparation, including the test implementation plan. 

Based on pre-test activities in support of V2VT1, researchers identified a target speed of 21 mph 

±1 mph that would meet test objectives, with some margin of error. The actual test speed was 

only 19.3 mph, less than the minimum expected speed of 20 mph. At 19.3 mph, the kinetic 

energy of the impact is only 93 percent of that at 20 mph, and only 84 percent of that at 21 mph 

(the target speed). The test was successful in that the various components performed as designed, 

and the stroke of the PBC deformation tube appeared to have been exhausted. However, there 

was not enough energy to fail the shear bolts of the PBC. Researchers identified two 

discrepancies between the test conditions and the model as factors that led to recommended 

target collision speeds being lower than they otherwise would have been, and thus also 

contributed to insufficient collision energy to cause the shear bolts to fail. Post-test assessment of 

damage uncovered one issue regarding the design of the CEM locomotive support structure that 

needed to be addressed prior to V2VT2. Post-test FE analyses conducted at the actual test speed 

were in very good agreement with the test data, an indication of the reliability and fidelity of the 

FE models. 

Due to the COVID-19 pandemic, V2VT2 was postponed approximately 18 months. 

Pre-test support for VTVT2 focused on modifying the FE model to address the repairs made, 

modifying the cab car model and adding a freight car. Researchers made several modifications to 

the FE models to improve their fidelity.
2 

Pre-test simulations of VTVT2 indicated the couplers must be closed for the PBC system to 

exhaust the stroke of the deformation tube and fail the shear bolts. A target speed of 33 mph ± 2 

mph was chosen to meet test objectives of complete PBC stroke with shear bolt failure and 

energy absorption in the DAC of at least 50 percent of the design specification, with some 

margin for error. Due to the removal of the original flooring in the asbestos remediation process, 

the models indicated the collision forces that would arise in this test might challenge the 

buckling resistance of the cab car.

The actual collision speed was 32.8 mph – very close to the target. The test was successful, with 

all of the key test objectives met, including exhaustion of the PBC deformation tube stroke and 

failure of the shear bolts. The colliding vehicles did not derail, nor did one override the other. 

However, the cab car was “crippled,” with a large buckle forming in the underframe just forward

of the rear side doors. After impact, the wheels of the rear truck of the cab car lifted slightly and 

fell back onto the rail without causing a derailment. Overall, the vehicle-to-vehicle impact tests 

together were successful in demonstrating the effectiveness of the components of the CEM 

system working in tandem to absorb impact energy and to prevent override in two different

vehicle-to-vehicle collision scenarios.
3 

1. Introduction

Research to develop new technologies for increasing the safety of passengers and crew in rail 

equipment is being directed by the Federal Railroad Administration (FRA) Office of Research, 

Development, and Technology (RD&T). To that end, two crash energy management (CEM) 

components that can be integrated into the end structure of a locomotive have been developed: a 

push-back coupler (PBC) and a deformable anti-climber (DAC). These components are designed 

to inhibit override in the event of a collision. The results of vehicle-to-vehicle override, where 

the strong underframe of one vehicle, typically a locomotive, impacts the weaker superstructure 

of the other vehicle, can be devastating and compromise the occupied space. The objective of 

this research project is to demonstrate the feasibility of using these components to improve 

crashworthiness of equipped locomotives in a wide range of potential collisions, including 

collisions with conventional locomotives, conventional cab cars, and freight equipment. 

1.1 Background

RD&T and the Volpe National Transportation Systems Center (Volpe Center) continue to 

evaluate new technologies for increasing the safety of rail passengers and crew. In recognition of 

the importance of override prevention in train-to-train collisions in which one of the vehicles is a 

locomotive [1][2][3], and in light of the success of crash energy management technologies in 

passenger trains [4], FRA seeks to evaluate the effectiveness of crashworthy components that are 

integrated into the end structure of a locomotive. These components are specifically designed to 

mitigate the effects of a collision and, in particular, to prevent override of one of the lead 

vehicles onto the other [5]. 

In prior Volpe Center research, designs for two CEM components for retrofit onto the forward 

end of a locomotive, a DAC and PBC, were developed, fabricated, and tested [6][7]. The 

performance of each design was evaluated through large deformation dynamic finite element 

(FE) analysis. Two test articles were fabricated and dynamically tested individually by means of 

a railcar impact into a test wall to independently verify performance characteristics of the two 

components relative to specific requirements. The tests were successful in demonstrating the 

effectiveness of the two design concepts. Test results were consistent with FE model predictions 

in terms of energy absorption capability, force-displacement behavior, and modes of 

deformation. 

In a follow-on program, the two CEM components were integrated into the end structure of a 

conventional locomotive (see Figure 1) to demonstrate, through a series of full-scale vehicle 

collision tests, that these components work together to mitigate the effects of a collision and 

prevent override [8]. Each of these tests were designed to evaluate the performance of the CEM 

locomotive in head-on collision scenarios in which a moving CEM locomotive (or CEM 

locomotive-led consist) collides with a stationary vehicle or consist. The stationary vehicle (or 

lead vehicle in a consist) may be a conventional locomotive, a CEM locomotive, a cab car, or a 

freight car. The overall objective of these tests is to demonstrate the effectiveness of a 

locomotive CEM system comprised of a PBC and a DAC. 
4 

Figure 1. CEM locomotive comprising a DAC and PBC retrofit onto an F40 locomotive 

In a first series of tests, both conventional and CEM coupling tests were conducted. The 

conventional coupling tests, between a conventional locomotive and a standing M1 cab car, were 

conducted to establish the speed at which coupling does not cause damage to either of the 

colliding vehicles [9][10]. The CEM coupling tests evaluated the performance of the PBC at 

collision speeds ranging from 2 mph to 9 mph [9]. In these tests, the CEM locomotive impacted 

a standing M1 cab car. Two reports detail the test instrumentation and provide the raw test data 

for both the conventional [10] and CEM coupling tests [11].

In this program, sub-contractor CAMX (formerly TIAX) provided consulting services to the 

Volpe Center in support of two vehicle-to-vehicle collision tests — one with a CEM locomotive 

impacting a standing conventional locomotive, and one with a CEM locomotive impacting a 

standing consist led by an M1 cab car with trailing freight cars. These services included FE

analyses, review of test implementation plans, troubleshooting of the CEM systems used in the 

tests, post-test data review, and repair recommendations for the equipment. 

1.2 Objectives

The objective of this effort was to provide engineering evaluation and program management, 

including FE analyses and troubleshooting, for two CEM locomotive vehicle-to-vehicle tests. 
5 

Prior to the tests, these services included making modifications to FE models, as needed, and 

simulation of test collisions to help determine test parameters (particularly impact speed) and to 

predict the behavior of the vehicles during the impact. The services also included solving 

structural and logistical issues that arose with the CEM components and their retrofit to the 

locomotive. Following each test, these services included evaluation of test results, evaluation of 

vehicle damage, and recommendations for vehicle repair in preparation of subsequent tests. 

Vehicle-to-Vehicle Test 2 (V2VT2) was postponed approximately 18 months due to travel 

restrictions caused by the COVID-19 pandemic. 

1.3 Overall Approach

The approach to this effort was dependent on the nature of the issues that arose. In general, the 

approach included review of test plans, e-mail exchanges, telephone discussions, pre-test and 

post-test data and photographs of vehicle components, and the creation and execution of FE 

models simulating the two vehicle-to-vehicle tests. 

1.4 Scope

Researchers focused on providing engineering evaluation and program management for the two 

CEM locomotive vehicle-to-vehicle tests in support of the objectives outlined in Section 1.2. 

Prior to each test, Volpe Center and CAMX personnel participated in discussions and assisted 

with problem-solving of structural and logistical issues that arose with the vehicles. A key 

component of the effort was pre-test FE analysis of the impact tests to determine test parameters 

and to predict the behavior of the vehicles. Following each test, damage evaluations were 

performed, and repair recommendations were developed for the equipment. Retrofit design 

modifications necessary for the repair of these components and their attachment to the main 

structure of the locomotive were within scope of this program; however, such modifications were 

kept to a minimum. 

1.5 Organization of the Report

The remainder of this report is organized into eight sections that describe the activities in the test

program: 

• Section 2. Vehicle-to-Vehicle Test 1 Pre-Test Analysis 

• Section 3. Vehicle-to-Vehicle Test 1 Test Results

• Section 4. Vehicle-to-Vehicle Test 1 Post-Test Evaluation 

• Section 5. Vehicle-to-Vehicle Test 2 Pre-Test Analysis

• Section 6. Vehicle-to-Vehicle Test 1 Test Results

• Section 7. Vehicle-to-Vehicle Test 2 Post-Test Evaluation

• Section 8. Construction of Finite Element Models 

• Section 9. Conclusion 

Note that some of the FE model creation activities described in Section 8 were performed as part 

of Section 2 and Section 5 of the program. 
6 

2. Vehicle-to-Vehicle Test 1 Pre-Test Analysis

This section describes engineering evaluation and project management performed in support of 

the first CEM locomotive vehicle-to-vehicle test (V2VT1). These services culminated in a trip to 

the Transportation Technology Center (TTC) in Pueblo, Colorado, in January 2019 to witness 

Vehicle-to-Vehicle Test 1, a collision between a moving CEM locomotive and a standing 

conventional locomotive. The test was conducted by Transportation Technology Center, Inc. 

(TTCI), a wholly owned subsidiary of the American Association of Railroads (AAR), on behalf 

of FRA. A schematic of the test is shown in Figure 2. Details of the test preparation, test 

requirements, and instrumentation can be found in a companion ASME paper [12]. 

Figure 2. Schematic of CEM Vehicle-to-Vehicle Test 1 initial conditions

• Activities performed during this period included modification of FE models (described in 

greater detail in Section 8 of the report):

o Modification of the FE model of the CEM locomotive to include a more explicit 

representation of the coupler carrier so that impact between the coupler and the 

coupler carrier could be realized, as well as failure of the coupler carrier. 

o Modification of the FE model of the conventional locomotive to include a plow. 

o Revision of the FE model of the conventional locomotive to include modifications to 

the collision post and other structures in the short hood to reflect the pre-S-580 

condition of Locomotive 4117 that will be used in the upcoming collision test. 

• Assembly and implementation of an FE model reflecting these modifications for impact 

of the CEM locomotive with a conventional locomotive at approximately 20 mph. 

• Review and comment of the Test Implementation Plan (TIP) for the V2VT1 planned for 

January 2019. 

• Participation via telephone and e-mail in a number of discussions in preparation for the 

January 2019 test 

2.1 Pre-Test Finite Element Analysis 

An FE model originally constructed as part of a prior program [8] was modified to:
7 

(1) More explicitly model the coupler/coupler carrier interaction. 

(2) Incorporate differences between the conventional locomotive planned for use in V2VT1 

with the representative locomotive design used in the earlier program. 

These modifications are described in more detail in Section 8. One of the primary purposes of 

the model was to help determine the collision speed for the test. This speed was calculated to 

satisfy three key test objectives: 

(1) Exhaustion of push-back coupler (PBC) stroke. 

(2) Failure of the shear bolts connecting the sliding lug to the sides of the draft pocket. 

(3) Sufficient deformation of the deformable anti-climber (DAC) to absorb 50 percent of its 

specified energy absorption capacity of 600 ft-kips, i.e., 300 ft-kips. 

Based on the results of prior analyses, researchers determined that a collision speed of 20 mph 

was sufficient to satisfy these criteria. Results from FE analyses of a collision at this speed are 

summarized in the next several figures.

Figure 3 shows a side view of the model for this collision scenario. The model for the CEM 

locomotive employed approximately 230,000 elements, with the element size defined to be 

progressively smaller near the colliding interface. 

Figure 3. Side view of the model for a moving CEM locomotive (left) colliding with a 

conventional locomotive (right)

Figure 4 shows a side view of the colliding vehicle ends after 12.8” of crush (~0.04 seconds). At 

this point, the coupler carrier bolts had just failed after impact from the PBC. During the next 

~0.05 seconds, the coupler continued to push back until exhausting its stroke after approximately 

24.5” of crush (see Figure 5), causing the shear bolts to fail. At this level of crush, the upper 

DAC tube assembly had impacted the anti-climber of the conventional locomotive.

As the vehicles continued to crush, the load path shifted upward to the DAC, specifically the 

upper DAC tubes. The upper DAC tubes continued to crush against the anti-climber of the 

conventional locomotive, and the respective short hoods begin to crush. At the peak extent of 

crush (35”, see Figure 6), the vehicle ends were extensively engaged. Deformation of the 

respective vehicle ends is illustrated in Figure 7. Most of the deformation occurred in the upper 

DAC assembly, which crushed about 10” and rotated back as indicated, and in the central 

regions of the respective short hoods. A detail showing only the conventional locomotive plow 

and the CEM draft pocket side plates (Figure 8) indicates that there was a minimal, localized 

deformation of the plow due to impact with the front edges of the side plates, where the coupler 

carrier was mounted. Figure 9 shows a side view of the DAC at various stages of the collision.

Figure 10 shows the pre-test analysis calculated force-displacement curve, indicating the force 

contributions from the PBC, DAC, and other end structures. As indicated in the figure, coupler 

20 mph
8 

carrier failure occurred after ~12” of crush (~0.04 seconds after impact), DAC engagement 

occurred after ~20” of crush (~0.08 seconds after impact), and shear bolt failure occurred after

~24” of crush (~0.9 seconds after impact).

At the maximum extent of crush, the DAC absorbed approximately 420 ft-kips of energy, well 

above the target of 300 ft-kips. The exhausted PBC absorbed its design limit of almost 1,100 ftkips. Other structures in the end frames of the respective vehicles, including the conventional 

locomotive draft gear, absorbed another 300 ft-kips.

Figure 4. Detail showing colliding vehicle ends after 12.8” of crush; the coupler carrier 

bolts have failed 
9 

Figure 5. Detail showing colliding vehicle ends after 24.5” of crush; the shear bolts have 

now failed

Figure 6. Detail showing colliding vehicle ends after 35” of crush (peak displacement)

Failed Coupler Carrier 
10 

Figure 7. Deformation at 35” crush. Left — CEM locomotive; right — conventional 

locomotive 

Figure 8. Detail showing minimal deformation of conventional locomotive plow (red) at 35” 

crush due to impact with draft pocket side plates (blue)
11 

Figure 9. Deformation of DAC at various extents of crush

Note: elements with PEEQ > 0.3 have been removed. Not all such elements have failed, due 

to triaxiality dependence of failure criterion.

Undeformed 28.0” Crush 32.5” Crush 35.9” Crush
12 

Figure 10. Force-displacement curve showing contributions from PBC, DAC and other end 

structures 

2.2 Revised Pre-Test Analyses

Just prior to the test, informed by measurements of the actual weights of the instrumented CEM 

locomotive (233 kips) and conventional locomotive (257 kips), an FE analysis incorporating the 

measured weights was conducted at the target speed of 21 mph as well as at the limits of the 

expected speed range (20 mph and 22 mph). Selected results from theses analyses are presented 

in Figure 11 through Figure 13. Figure 11 shows the calculated force-displacement curve and the 

estimated contributions of the key structures for a 21-mph test speed. Results indicate that the 

predicted crush at 21 mph was about 37”, with the shear bolts failing at a crush of 25”. Figure 12

shows the respective vehicle speeds and indicate a crossover of speeds (corresponding to 

maximum crush) at ~0.19 seconds. Figure 13 shows calculated force-crush curves for three 

collision speeds — 20 mph, 21 mph and 22 mph — in the expected range for the test, with the 

predicted crush increasing from ~34” at 20 mph to ~39” at 22 mph. Since the desired impact 

speed was 20 mph, the target impact speed was set to 21 mph to take into account the ±1 mph 

speed tolerance. 

-200

0

200

400

600

800

1000

1200

1400

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0 10 20 30 40

Crush (in)

Force (1000 lbf)

DAC

End Structures

PBC

Total

Coupler 

Carrier Failure

DAC 

Engagement

Shear Bolt 

Failure

End Structure 

Crush
13 

Figure 11. FE model calculated force-displacement curve at 21 mph collision for revised 

model using measured vehicle weights, with estimated contributions of key components

Figure 12. FE model predicted vehicle speeds at 21 mph for revised model using measured 

vehicle weights

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0 10 20 30 40

Crush (in)

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DAC

End Structures

PBC

Total
14 

Figure 13. Comparison of revised FE model predicted force-displacement curves for 

collision speeds of 20 mph, 21 mph, and 22 mph

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Crush (in)

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15 

3. Vehicle-to-Vehicle Test 1 Test Results

Vehicle-to-Vehicle Test 1 was performed on January 23, 2019. The test locomotives were 

inspected on the afternoon of January 22. The instrumentation for the test was inspected. 

Positioning of strain gages on the underframes of the respective vehicles was verified. A report 

details the test instrumentation and provides the raw test data for this test [13]. Details and 

evaluation of the test results can be found in a companion ASME paper [14]. 

3.1 Test Outcome

On the day of the test, the weather conditions were clear with low winds. The research team

decided both couplers would be left open to increase the chance of coupling, and the couplers 

were aligned within 1 inch vertically. The conventional locomotive’s air brakes were applied, 

and the hand brake was secured before the impact. The target impact speed was 21 mph, and the 

actual impact speed was 19.3 mph. Figure 14 shows the vehicles after the test. The vehicles were 

kept in-line. There was no derailment of the vehicles and no sign of override. 

Figure 14. Post-test photo of the locomotives
16 

During the test, the couplers engaged at impact but did not lock together. The PBC triggered 

properly and moved back into the draft pocket. As the PBC moved back, the coupler carrier 

broke away, as designed. The intact coupler carrier before the test is shown in Figure 15. Figure

16 shows the failed coupler carrier where it fell after the PBC head moved back through it and 

disengaged it. 

Figure 15. Pre-test photograph of the coupler carrier

 

Figure 16. Post-test photograph showing the coupler carrier lying on the track

After pushing through the coupler carrier, the PBC continued to move back, deforming the crush 

tube. Figure 17 and Figure 18 show the back of the deformation tube of the PBC before and after 

the impact. The deformation tube was covered in paint that was designed to peel off in strips as 

the exterior tube deformed. Figure 18 indicates that the stroke of the deformation tube was 
17 

almost exhausted. Figure 19 shows the deformation tube after it was removed from the draft 

pocket. Measurements taken confirmed that the full design stroke of the deformation tube was 

nearly exhausted. This was confirmed by evidence of contact between the limit stop mounted on 

the sliding lug and the rear of the PBC head, as shown in Figure 20 and Figure 21. This contact 

was designed to occur at the full stroke of the PBC. 

Figure 17. Pre-test photograph of the back of the PBC deformation tube

Figure 18. Post-test photograph showing the back of the PBC deformation tube
18 

Figure 19. Deformed PBC deformation tube removed from the draft pocket; peeled paint 

has been removed

Figure 20. Damage to the limit stop mounted to the front of the sliding lug due to contact 

by the back of the PBC coupler head
19 

Figure 21. Damage to rear of the PBC coupler head from limit stop contact 

As the PBC was pushed back, the top DAC tubes impacted the front of the conventional 

locomotive and began to crush. Figure 22 shows the two locomotives engaged after the impact. 

The photo on the right shows that only the upper DAC tubes crushed; the lower DAC tubes did 

not deform, as expected. 

For comparison, Figure 23 shows the undeformed DAC before the test, and Figure 24 shows the 

deformed DAC after the test and after the vehicles had been separated. Figure 25 shows side 

views of both the right and left upper DAC tubes. The crush was greater on the right side than on 

the left — due to an approximately 2” lateral offset between the locomotives at the moment of 

impact. 

The shear bolts connecting the sliding lug to the draft pocket did not trigger; therefore, the 

sliding lug did not move back into the draft pocket. 
20 

5

Figure 22. Post-test photo of CEM system; close-up on the right

Figure 23. Pre-test photograph of DAC 
21 

Figure 24. Post-test photograph of DAC showing that only the upper DAC tubes deformed

Figure 25. Deformed upper DAC tubes, right and left sides, respectively
22 

3.2 Damage to the Equipment

Other than the damage to the CEM components, which was designed to occur, there was 

minimal damage to the CEM locomotive. Figure 26 shows the small amount of deformation of 

the bottom of the short hood. This was minor and easy to repair.

Figure 26. CEM locomotive damage 

There was also minimal damage to the conventional locomotive. Figure 27 and Figure 28 show 

the dent caused by interaction with the short hood of the CEM locomotive. This was also minor 

and easy to repair. 
23 

Figure 27. Conventional locomotive damage 

Figure 28. Close-up of conventional locomotive damage 

Figure 29 shows a comparison of post-test photographs that provide evidence of the lateral offset 

of the colliding vehicles: matching scratches on short hoods of CEM locomotive (top left) and 

conventional locomotive (top right) indicate a 2.5” lateral offset. This offset resulted in less 

extensive crush of the left upper DAC tube (bottom left) relative to crush of the right upper DAC 

tube (bottom right).
24 

Figure 29. Post-test photographs indicating lateral offset of the colliding vehicles
25 

4. Vehicle-Vehicle Test 1 Post-Test Evaluation

Immediately following the test, the test vehicles were inspected at the test site and measurements 

and photographs were taken. Both vehicles were then moved into one of the buildings, with the 

CEM locomotive positioned over a pit where additional measurements photographs were taken. 

Measurement of paint loss on the PBC deformation tube indicated that the permanent stroke was 

about 18.5”. This provided evidence that the shear bolts were just about to be loaded as the 

relative crush between the two vehicles reached its maximum. This was consistent with the 

presence of a scratch mark on the limit block that was added to the sliding lug to promote clean 

contact between the coupler and the sliding lug at the end of deformation tube stroke. 

4.1 Data Review and Analysis

Test data were compiled and filtered by TTCI and provided to the Volpe Center and CAMX in a 

spreadsheet. The data (from accelerometers, string potentiometers, strain gages, and cameras) 

were reviewed relative to what they reveal about the impact sequence, vehicle motions, collision 

forces and strain near the shear bolts. Key results are summarized in several time-history plots. A 

report details the test instrumentation and provides the raw and filtered test data [13]. Post-test 

filtering of the data was performed using a two-pass, phaseless, four-pole digital filter algorithm 

consistent with the requirements of SAE J211 (CFC 60). 

4.1.1 Impact Sequence

Inspection of accelerometer and strain gage data (see Figure 30) indicated that full engagement 

of the colliding open couplers did not occur until approximately 0.031 seconds after initial 

impact. At a collision speed of 19.3 mph, the 0.031-second lag between the time at which the 

impact tape mounted to the front surface of the conventional locomotive coupler was triggered 

and the time at which the couplers were fully engaged and began to transmit significant 

longitudinal forces indicated additional travel of approximately 10.5”. 

Figure 30. Left — carbody longitudinal accelerations (orange for stationary, blue for 

moving); right — strain at the top of the CEM coupler shank 

-7.0

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Acceleration (

g)

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ASUC_X AMUC_X

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Microstrain

Time (sec)

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0.031 sec 0.031 sec

Car Body Accelerations Strain at Top of CEM Coupler Shank
26 

String potentiometer data (see Figure 31, left) indicated that the upper DAC assembly impacted

the skirt of the conventional locomotive after about 0.075 seconds. Note the delay of about 0.005 

seconds between the initiation of motion on the left and right sides. Data from longitudinal 

accelerometers positioned at the center of the CEM locomotive carbody (see Figure 31, right) 

also indicate a significant jump after 0.075 seconds, accompanying the impact of the anticlimbers.

Figure 31. Left — upper DAC deformations; right — carbody longitudinal accelerations 

The carbody acceleration pulse dropped to near zero after about 0.175 seconds (see Figure 32). 

There did not appear to be any additional pulses associated with impact of the coupler with the 

sliding lug.

0.075 sec

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Displacement (in)

Time (sec)

DMACTR_X Inch DMACTL_X Inch

0.075 sec

Upper DAC String Pots Car Body Accelerations

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Acceleration (

g)

TIme (sec)

ASUC_X AMUC_X

0.175 sec
27 

Figure 32. Carbody longitudinal acceleration pulse drops to zero after about 0.175 second

4.1.2 Vehicle Motions 

Integrating the acceleration pulses for the respective vehicles and imposing a 19.3 mph initial 

speed for the CEM locomotive yielded speed and displacement time-histories (see Figure 33).

Figure 33. Successive integration of the acceleration pulses (top row) for the CEM 

locomotive (left) and conventional locomotive (right) yielded speed (middle row) and 

displacement (lower row) time-histories

Plotting the vehicle speed curves together indicated that the maximum crush of the vehicles 

occurred after about 0.157 seconds, shown in Figure 34. After this, the vehicles rebounded

elastically. Note also the abrupt change in the rate of decrease in CEM locomotive speed at 0.075 

second due to the impact of the DAC. 

Calculated relative vehicle displacement and crush time-histories are plotted at the left in Figure 

35. Relative vehicle displacement peaks after 0.157 seconds at 34.1”. Subtracting the 

displacement prior to full coupler impact yielded a peak crush distance of 23.6”. This 10.5” 

difference was consistent with the travel (~11”) that occurred when the couplers were open and 

the knuckles moved past one another and rotated before the respective vehicles fully engaged 

(see schematic in Figure 35, right). TTCI has verified these distances. Note that the precise 

distance of travel prior to full coupler engagement was likely affected by the alignment of the 

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Acceleration (g)

TIme (sec)

ASUC_X

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Displacement (in)

Time (sec)

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Speed (mph) -30.0

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Displacement (in)

TIme (sec)

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Acceleration (g)

Time (sec)

AMUC_X

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Speed (mph)
28 

couplers at impact and the positioning and thickness of the impact sensor bundle. Figure 36

shows a pre-test photograph of the couplers (left) and a photograph of the conventional 

locomotive coupler with the impact sensors taped to the front surface of the knuckle, just prior to 

running the test (right). Note also that one of the two couplers shown at left appears to have been

closed.

Figure 34. Calculated vehicle speed time-histories

Figure 35. Left — calculated relative vehicle displacement time-histories; right — 

schematic illustration of additional vehicle approach prior to force build-up after initial 

impact when couplers are open

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25

Speed (mph)

Time (sec)

CEM Locomotive Conventional Locomotive

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2 0.25

Displacement (in)

Time (sec)

Relative Displacement Crush

~7” ~11”
29 

Figure 36. Top Left — a pre-test photograph of the couplers from above; bottom left — 

impact sensors affixed to the front surface of the stationary conventional locomotive; right 

— impact sensors affixed to the front surface of the CEM locomotive coupler 

Test videos indicated a noticeable cyclic pitch (bouncing) of the CEM locomotive carbody on the 

suspension system of the forward truck during the collision. The vertical travel was much larger 

than anticipated, as the truck suspension is meant to have a limit stop of ±2”, which was included 

in the FE model. The vertical acceleration pulse for the CEM carbody at the forward truck (see 

Figure 37, upper left) was integrated to estimate the speed time-history at this location (see 

Figure 37, lower left). This curve was then corrected (see Figure 37, upper right) to remove drift 

(a common issue with these types of data) by reasoning that this curve must be near zero both at 

impact and after 5 seconds, when the oscillations had damped out. Finally, the corrected speed 

curve was integrated again to estimate the vertical displacement time-history at this location (see 

Figure 37, lower right). The displacement curve indicates an initial downward displacement of 

about 4.5” followed by continued oscillation, with an approximate magnitude of about 3” that 

slowly decreases over the next several seconds.
30 

Figure 37. Upper left — vertical acceleration of carbody at CEM forward truck; lower left 

— integration of acceleration pulse to yield vertical speed (in mph); upper right — 

correction of speed curve to remove drift; lower right — integration of corrected speed 

curve to yield vertical displacement time-history

4.1.3 Collision Forces

The longitudinal acceleration can be multiplied by the mass of the CEM locomotive (232,600 

lbs) to get an estimate of the longitudinal force, as shown in Figure 38. The resulting curve 

indicates that the force increased considerably — from an average of about 450 kips to an 

average of about 1,000 kips — when the DAC assembly was impacted. The huge peak in force 

after initial impact (almost 1,400 kips) and the oscillation during push-back suggest that this 

measure of forces must be considered approximate, at best, as it depends on the vehicle acting as 

a single-degree-of-freedom system.

Based on results from coupler impact studies [12], a better estimate of the force through the 

push-back coupler is derived from the longitudinal strains in the coupler shank. Figure 39 (left) 

shows estimated time-histories of the force through the coupler based on data from the five strain 

gages positioned on the shank (top, left, and right) and a few inches forward of the pin (left and 

right). The data from the five gages were somewhat noisy, so averages of the forces for the three 

front gages (shank) and two rear (pin) gages, as well as the overall average, were calculated. 

Figure 39 (right) shows the calculated averages over the first 0.08 seconds after impact. 

Compared to the acceleration-based estimates of force, these strain gages provided a more 

reasonable estimate of force when all of the force was going through the coupler (i.e., prior to 

DAC impact). The jump in force at impact was much smaller, and the plateau force was much 

more consistent with the rated push-back load of 674 kips for the PBC. 

-10

-8

-6

-4

-2

0

2

4

6

8

0 1 2 3 4 5

Acceleration (G's)

Time (sec)

AMLE_Z G's

-1

0

1

2

3

4

5

0 1 2 3 4 5

Speed (mph)

Time (sec)

VMLE-Z 

-2.5

-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

0 1 2 3 4 5

Speed (mph)

Time (sec)

VMLE-Z - Corrected

-5.0

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

5.0

0 1 2 3 4 5

DIsplacement (in)

Time (sec)

DMLE-Z - Corrected 

Vertical Motion at CEM Truck

The corrected curve was obtained by factoring out 

integration drift by reasoning that the speed must 

be near zero at time zero and also after 5 seconds
31 

Figure 38. Force time-history based on single-degree-of-freedom approximation (F = ma) 

where ‘m’ is the mass of the CEM locomotive and ‘a’ is the longitudinal acceleration at the 

center of the vehicle

Figure 39. Left — estimated time-histories of the force through the coupler based on data 

from strain gages positioned on the shank and near the pin; right — calculated averages 

forces for the three front (shank) and two rear (pin) gages overs the first 0.08 seconds after 

impact

-200

0

200

400

600

800

1,000

1,200

1,400

1,600

0 0.05 0.1 0.15 0.2 0.25

Force (kips)

Time (sec)

1000 kips

450 kips

The apparent magnitude of the initial peak in force is likely an 

artifact of the 1-D approximation of the acceleration pulse.

-600

-400

-200

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2 0.25

Force (kips)

Time (sec)

F-SMCST F-SMCSR F-SMCSL F-SMCPR F-SMCPL

-200

0

200

400

600

800

1000

1200

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08

Force (kips)

Time (sec)

Average Average Front Average Rear

The strain-based estimate of the initial peak in force is 

noticeably lower than the acceleration-based estimate.
32 

4.1.4 Strain Near Shear Bolts

Strain gage readings for the draft pocket and sliding lug bolt hole regions were consistent with 

results from the coupling tests [12]. 

Table 1 reports averaged values (front and rear, top and bottom, and left and right sides) for the 

eight gages mounted to the draft pocket side plates and the eight gages mounted to the sliding lug 

slide plates. (Note that positive readings indicate compression.) Reported values for the gages 

mounted to the draft pocket side plates (about 1” behind each shear bolt) indicated that the strain 

levels were relatively uniform, with little variation of averaged values front-to-back, side-to-side, 

and top-to-bottom.

Sliding lug side plate strains were generally much smaller than draft pocket side plate strains, 

making it difficult to infer trends from the data. It did appear, however, that the strain levels were 

very different front-to-back, with the front gages indicating compression and the back gages 

indicating tension. It was not immediately evident why these strain magnitudes changed sign, but 

it should be noted that previous testing and analysis on stiff bolted rail components have 

indicated that the transmission of force through the bolted connections can be quite complex [3]. 

Figure 40. Left — time-histories of strain behind the eight top and bottom shear bolts on 

the draft pocket side plates; right — time-histories of strain ahead of the eight top and 

bottom shear bolts on the sliding lug side plates

-200

0

200

400

600

800

1000

1200

0 0.05 0.1 0.15 0.2 0.25

Microstrain

TIme (sec)

SMDP1 um/m SMDP2 um/m SMDP3 um/m SMDP4 um/m

SMDP5 um/m SMDP6 um/m SMDP7 um/m SMDP8 um/m
33 

Table 1. Comparison of averaged measured peak strain levels (microstrain) during vehiclevehicle test with those from 9-mph coupling test; note that positive strain gage readings are 

compressive

Location Test

Bolt Hole Locations

Front Rear Left Right Top Bottom 

Draft Pocket Side 

Plate

20 mph 

Impact Test 550 670 530 700 600 630

9 mph 

Coupling 

Test

380 530 550 360 490 430

PBC Side Plate

20 mph 

Impact Test 80 -130 -40 0 -20 -20

9 mph 

Coupling 

Test

40 -150 -40 -60 -30 -70

4.2 Comparison of Test Results with Pre-Test Model Predictions

Pre-test predictions of behavior during the test are compared with test results in this section. 

Differences between model predictions and test results can be largely attributable to two key 

factors:

1. The actual collision speed was 19.3 mph — a 16 percent decrease in collision energy when 

compared to the target speed of 21 mph and a 7 percent decrease in collision energy when 

compared to the minimum expected collision speed of 20 mph. 

2. Having the couplers open brought the DAC system much closer (~11”) to impact with the 

conventional locomotive end frame prior to PBC impact; it therefore absorbed much more 

energy prior to shear bolt failure. 

A few modeling issues were revealed as a result of the comparison with test results. For the most 

part, these likely had a minor influence on results, but identifying them can help improve future 

simulations. Of these, the issue that likely had the most influence on results was the use of shell 

elements to model most of the vehicle structures. It is difficult to account for certain thicknesses 

of structures when modeling vehicle contact using shell elements. In particular, the upper DAC 

assembly protruded outward by 20.875” from the end plate, but in the model this distance was 

only modeled as 19.5” because the 1”-thick front plate and the 0.375” back bearing pad were 

modeled as shell elements, reducing the extent that the upper DAC assembly protruded forward 

off the end plate of the CEM locomotive. This 1.375” difference added to the 10.5” difference 

attributable to open coupler impact, so the DAC impact occurred about 12” sooner than the 

model would indicate. As a result, much of the collision energy that otherwise would have been
34 

directed into the PBC was instead directed into the DAC, increasing the collision speed needed 

to fail the shear bolts.

With these issues in mind, several comparisons between model predictions and test results are 

highlighted below.

4.2.1 Vehicle Motion

Comparing the relative displacement (or crush) and speed time-histories derived from test results 

with model predictions (Figure 41) indicated that the CEM locomotive slowed down more 

quickly than pre-test model results would indicate, especially when the first 0.031 seconds after 

impact are neglected (allowing the open couplers to fully engage). This difference in behavior 

was indicative of higher collision forces and became more pronounced at about 0.075 seconds 

when the DAC tubes began to crush. These differences were likely attributable to the much

earlier impact of the DAC (relative to the extent of PBC crush) during the test than was modeled, 

as noted above. Accounting for the 10.5” travel of the couplers prior to impact in the model, as 

well as the 1.375” additional protrusion of the DAC, as noted, will likely improve agreement.

Figure 41. Left — comparison of measured displacement time-histories with model 

predictions; right — comparison of measured speed time-histories with model prediction

4.2.2 Force-Displacement Curve

Figure 42 shows the force versus crush through the carbody and through the coupler, from both 

the pre-test prediction and the test data. The solid blue line is the accelerometer-based force from 

the longitudinal center of the underframe. The solid red line is the strain-based force from the 

coupler shank, which gives a better estimate of the force through the push-back coupler. As seen 

in the figure, the average force through the CEM locomotive carbody (solid blue line) increases 

considerably — from an average of about 450 kips (when the PBC deformation tube alone was 

absorbing energy) to an average of about 1,000 kips (when the DAC assembly was impacted). 

While the estimated carbody force was about 450 kips during the PBC deformation, the coupler 

force (solid red line) was approximately 670 kips — the designed force level for PBC pushback. 

A comparison of test/model force-crush behavior (Figure 42) indicates that, in the test, the DAC 

tubes began to absorb collision energy much earlier than in the model. As noted, this was 

Vehicle Crush

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2 0.25

Displacement (in)

Time (sec)

Test - Relative Displacement Test Crush-Shifted Model Crush (20 mph)

Vehicle Speed

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25

Speed (mph)

Time (sec)

Test - CEM Locomotive Test - Conventional Locomotive

Model - CEM Locomotive Model - Conventional Locomotive
35 

primarily due to the 10.5” or so of travel prior to loading the push-back coupler system, which 

caused the DAC assembly to engage earlier relative to PBC crush.

Note that while the early engagement of the DAC likely prevented shear bolt failure at this test 

speed, it nonetheless contributed significantly to energy absorption. 

Figure 42. Left — comparison of calculated test/model force crush curves (coupler only and 

total) 

4.2.3 Energy Absorption

Calculated/estimated energy absorption totals for the test and the model are compared in Table 2. 

The PBC stroke was limited to 21”, but 2.7” of that was compression of the PBC draft gear. 

Assuming that the full stroke of the PBC was exhausted during the test, as evidenced by the 

scratch on the limit stop, then the model and test values for these energies were, for all intents 

and purposes, equal. The extent of energy absorption in the PBC and conventional locomotive 

draft gears was estimated by subtracting the design deformation tube energy (1,030 kips) from 

the FE model calculation of energy for the connector elements representing the PBC and the 

conventional locomotive draft gear. Note that each of the draft gears absorbed about 70 ft-kips of 

energy. 

-800

-600

-400

-200

0

200

400

600

800

1,000

1,200

1,400

1,600

0 5 10 15 20 25 30

Force (kips)

Crush (in)

Test - Strain-Based Coupler Force Test - Accel-Based Force

Model - Coupler Force Model - Total Force
36 

Table 2. Comparison of calculated energy absorption levels from the test with model 

predictions

Component Test

(ft-kips)

Model

(ft-kips)

PBC Deformation Tube 1,0301 1,0301

PBC/Conventional Locomotive 

Draft Gears 1402 1402

DAC 2603 3406

Other Vehicle End Structures 704 2006

Total 1,5005 1,7106

1. 675 kips x 18.3” stroke (remaining 2.7” PBC stroke prior to bolt failure is in draft gear)

2. Model calculation of total PBC energy minus deformation tube energy — assumed to be the 

same for the test. 

3. Estimate based on model DAC energy × test DAC stroke/model DAC stroke (340 x 10/13.5)

4. Subtraction of DAC and PBC energy from total energy

5. Integration of area under acceleration-based force vs. displacement curve

6. Model calculation of respective energies

4.2.4 Strain Near Shear Bolts

A contour plot of longitudinal strain in the draft pocket side plate (see Figure 43) during PBC 

pushback indicates that the model predicted smaller strain levels than were measured in the test 

(see Table 1). The strain levels were greater near the forward bolt holes — also contrary to test 

results which indicate that they were about the same. Note that the use of connector elements to 

define the shear bolts likely detracted from the accuracy of predicted strain levels in the region of 

the bolts, as it was difficult to determine their influence on the stiffness of the structures

surrounding the bolts.
37 

Figure 43. Left — contours of strain on the side of the draft pocket during deformation 

tube stroke

4.2.5 Mode of Deformation

The predicted mode of deformation of the top DAC assembly appeared to be very consistent 

with test results, as shown in Figure 44. The model did not, of course, pick up the side-side 

variation in crush due to the ~2” lateral motion following impact. The much greater predicted

extent of crush of the nose of the short hood was consistent with the much more extensive 

predicted crush of the DAC (13.5” in the FE model vs. 10” in the test) due to the higher target 

speed versus actual test speed. 

Figure 44. Comparison of FE model prediction of CEM end frame mode of deformation 

with post-test photograph of the end frame (right)
38 

4.3 Comparison of Test Results with Post-Test Model Predictions

Informed by the post-test data review/analysis and inspection of the damaged vehicles, a few 

modifications were made to the FE model for V2VT1: 

• The impact speed was lowered to 19.3 mph. 

• The DAC tubes and angled gusset plates were extended by 1.125” so that the distance 

between the DAC and the conventional locomotive end frame matched that of the test. 

The extensions were modeled to be effectively rigid so that they did not change the 

energy absorption characteristics of the DAC. This modification is described in detail in 

Section 8.4. 

• The initial position of the CEM locomotive was adjusted so that, at impact of the fully 

engaged couplers, the end structures of respective vehicles were the appropriate distance 

from one another. At impact, the vehicle end plates were assumed to be 53.5” from one 

another. This distance was based on lengths of 31” and 28.5”, respectively, for the CEM 

locomotive and conventional locomotive couplers, with coupler pins positioned 3.5” 

behind the respective end plates, and a 1” gap between the locomotives (53.5” = 28.5” + 

31” – 2 × 3.5” + 1”). This was modified because the couplers were open for the test, as 

opposed to closed for the pre-test analysis. In the test, the couplers were not fully 

engaged until approximately 0.031 seconds. 

• The connector that governs impact of the two vehicles was modified so that the impact of 

fully engaged couplers occurred at approximately 0.031 seconds, as in the test (after 

~10.5” of free CEM locomotive travel following initial impact). 

FE model predictions for relative vehicle displacement, vehicle speed, and force-vs.-crush are 

compared with test results in Figure 45 through Figure 47. Predictions of relative vehicle 

displacement (Figure 45) compare quite favorably to test results, with the prediction of final 

vehicle crush only about 1” different than the test result. Similarly, predictions of vehicle speeds 

(Figure 46) are in excellent agreement with test results, particularly with respect to the time at 

which the vehicle speeds were determined to be equal (at maximum relative displacement).
39 

Figure 45. Comparison of revised FE model prediction of relative vehicle displacement 

with test results

Figure 46. Comparison of revised FE model prediction of vehicle speeds displacement with 

test results

Comparison of the predicted force-crush curve with test results (Figure 47) was a little more 

difficult because the force-crush curve for the test was not measured but had to be calculated 

from acceleration or strain data based on simplifying assumptions regarding vehicle behavior, as 

discussed in Section 4.2.2. Again, the solid red line is the strain-based coupler force, the solid 

blue line is the acceleration-based force at the CG of the CEM locomotive, the red dashed line is 

0

5

10

15

20

25

30

35

40

0 0.05 0.1 0.15 0.2 0.25

Displacement (in)

Time (sec)

Test Revised FEA - 19.3 mph

0

2

4

6

8

10

12

14

16

18

20

0 0.05 0.1 0.15 0.2 0.25

Speed (mph)

Time (sec)

Test - CEM Locomotive Test - Conventional Locomotive

Model - CEM Locomotive Model - Conventional Locomotive
40 

the model coupler force, and the dashed blue line is the model total force. As seen in the figure, 

the initial peak in the strain-based force (solid red line) indicates the coupler impact. The 

acceleration-based estimate (solid blue line) of peak force at impact was delayed with respect to 

the strain-based estimate. The acceleration-based estimate of force was not as reliable as the 

strain-based estimate of force, particularly in the early stages of the collision. It relied on the 

assumption that the locomotive was behaving as a single-degree-of-freedom system, with force 

equal to mass multiplied by acceleration. When the vehicles first impacted one another, the 

effective mass associated with the measured acceleration of the vehicle center of gravity was 

likely much lower than the total mass of the locomotive. However, the acceleration-based 

estimate was more reliably predicting the total force by the time the DAC was engaged. 

Figure 47. Comparison of FE model prediction of force-vs.-crush with values calculated 

based on test results

There was good agreement between the model and the strain-based measurement during the 

compression of the draft gears of both locomotives. Then the PBC triggered and the deformation 

tube began to crush. Again, there was good agreement here between the model and the strainbased measurement. Once the DAC was impacted by the conventional locomotive, the force 

levels increased. This was captured by the model and the acceleration-based measurement, but 

not in the strain-based measurement through the coupler shank, as expected. The force levels and 

the fluctuation in amplitude due to the DAC tubes deforming were very similar when comparing 

the model and the acceleration-based measurement. The model results also indicate a build-up of 

force near the end of crush, indicating the load on the shear bolts was increasing, but not by 

enough to cause failure.

The post-test predictions of force-crush behavior were in much better agreement than pre-test 

predictions due to the modification of the collision speed, the correction of the distance the DAC 

0

200

400

600

800

1,000

1,200

1,400

1,600

0 5 10 15 20 25

Force (kips)

Crush (in)

Test - Strain-Based Coupler Force Test - Accel-Based Force

Model - Coupler Force Model - Total Force

Compression 

of Draft Gears

Initiation of 

Deformation 

Tube Crush

DAC Impact

Impact of 

Couplers

Acceleration-based estimate of peak force at impact is delayed 

with respect to strain-based estimate. It is likely not accurate due 

to assumption of participating mass/filtering effects.

Sliding Lug 

Impact

Build-Up of 

Shear Bolt 

Load but No 

Failure
41 

extended forward of the end plate, and accounting for the period of free travel that followed

initial impact/triggering of impact tape sensors prior to full coupler engagement.

Aside from the PBC deformation tube, most of the deformation that occurred was, by design, 

concentrated in the DAC. Predictions of DAC deformation are compared with test results in 

Figure 48. As is evident, the model appeared to capture quite well the deformation of the upper 

DAC tubes, which crushed and rotated upwards during the collision. The deformation at the 

center of the DAC was predicted to decrease the distance from the DAC plate to the end plate of 

the locomotive from 18.875” to about 6.5”, i.e., about 12.4” of crush. The post-test measured 

distance was determined to be about 7.5” at this location, indicating a total crush of about 11.4”. 

Part of this 1” difference may be attributable to the lateral offset of the impact. 

The FE model also predicted some deformation of the conventional locomotive anti-climber 

gusset plates, as illustrated in Figure 49. This did not appear to have occurred during the test. 

At the time of this post-test FE analysis, TTCI researchers had not removed the collision posts to 

inspect damage to the supporting structures. When they did so, they discovered some damage 

where the angled gusset plate of the DAC was welded to the end frame. The FE model also 

predicted damage in this area. This is discussed further in the next section. 

Figure 48. Comparison of predicted DAC deformation with test results

Distance to front plate: ~6.5” Distance to front plate: ~7.5”
42 

Figure 49. Predicted deformation of conventional locomotive anti-climber apron and inner 

gusset plates 

Overall, the agreement between model predictions and test results was good: 

• The timing of DAC engagement was similar. 

• The extent of push-back coupler deformation was similar. 

• The mode of DAC deformation was similar; note that the FE model predicted build-up of 

shear bolt force to about 80 kips in each bolt, indicating they were very close to failing 

(88 kips) but did not fail.

There were a few potential causes for the small discrepancies present, including: 

• Different extents of conventional locomotive draft gear compression prior to load buildup to 674 kips 

• The actual strength of DAC component materials versus that modeled

• Lateral offset of the vehicles (appeared to be 2” to 3”) 

• Extra pitching of the CEM locomotive due to the lack of limit stops on the forward truckto-body connection 

• Underframe height mismatch (the CEM locomotive appeared to be about 3” higher) 
43 

4.4 Assessment of CEM Locomotive Damage/Repair Needs

Due to the low impact speed, damage to the CEM locomotive was limited. Following a post-test 

inspection of the vehicle, the following replacement/repair activities were recommended in 

preparation for the next test, Vehicle-to-Vehicle Test 2 (V2VT2): 

• Replace the PBC.

• Replace the shear bolts and bushings. 

• Inspect the sliding lug and draft pocket for damage. 

• Replace the upper DAC assembly. 

• Replace the coupler carrier. 

• Design and fabricate a retention system for the coupler carrier so it does not fall onto the 

track during a collision. 

• Inspect the upper DAC support structures and the modified collision posts. 

• Repair the short hood nose and apron side plates. 

After removing the DAC assembly and inspecting the DAC support structures, one further area 

of damage was revealed where the angled, upper DAC support plate on the left side of the CEM 

locomotive was welded to the front plate, as is illustrated on the left in Figure 50. The front plate 

did not have a doubling plate at this location, as it did behind the DAC tubes. There was clear 

evidence of damage at the top of the welded connection between the angled support plate and the 

end plate, as shown at right in Figure 50. 

Figure 50. Left — photograph showing cut-away left upper DAC tube and angled support 

plate; right — detail showing damage at top of connection between angled support plate 

and front plate

Cut-Away Upper 

DAC Tube

Cut-Away Angled 

Support Plate
44 

The damage in this area was consistent with pre-test model predictions which indicated high 

levels of plastic strain in this region prior to folding of the angle support plates, as shown in 

Figure 51.

Figure 51. Detail of deformed CEM locomotive at the end of the simulation of V2VT1 

showing plastic deformation at the top of the welded connection of the angled support plate 

to the end plate, as indicated

4.5 CEM Locomotive Repair

As noted in Section 4.4, when the damaged upper DAC assembly was removed from the CEM 

locomotive after V2VT1, damage was evident where the DAC angled support plates were 

welded to the end plate. 

Following discussions with the Volpe Center and CAMX, site technicians suggested and later 

implemented two modifications to remediate this issue. The first was to weld a 0.375”-thick 

bearing plate, as outlined in yellow at the left in Figure 52, onto the end plate. This plate, which 

extended upward a little beyond the level of the floor, would be welded to the front of the end 

plate along its sides and bottom and welded to the back of the front plate along its top. The 

second modification was to install a 1”-thick by 4”-wide by 9”-tall plate, oriented as shown in 

red at the right in Figure 52, behind the end plate of the locomotive at the location where the 

angled support gusset was welded to the front of the end plate. 

The FE model of the CEM locomotive was updated to include these modifications, as is 

discussed in Section 4.4. Note that, since the post-test FE analysis had already been conducted 

when these repairs were made, the FE analysis for the V2VT1 collision was not re-run. Based on 

the very localized area of damage, it is not likely that these modifications would have had a 

significant effect on the results of the analysis. 
45 

Figure 52. Left — outline of the bearing plate which will be welded to the front of the CEM 

locomotive end plate and onto which the angled gusset will be welded; right — illustration 

of the reinforcement gusset to be welded behind the end plate where the angled gusset plate 

was welded to the end plate

In addition to these repairs, the PBC was replaced, and the coupler carrier was rebuilt. Small 

cables were connected to the sides of the coupler carrier to prevent its interfering with 

instrumentation wiring or falling to the ground after failing and becoming a derailment trigger. 

Inspection of the draft pocket and sliding lug bolt holes revealed minimal damage. 

Further damage to the CEM locomotive was also minimal and included a small dent in the nose 

of the short hood. 
46 

5. Vehicle-to-Vehicle Test 2 Pre-Test Analysis

This section describes engineering evaluations and project management performed in support of 

V2VT2, conducted November 17, 2021, at TTC. In this test, a moving CEM locomotive collided 

with a standing consist comprising a cab car and two trailing hopper cars. A schematic of the test 

is shown in Figure 53. 

Figure 53. Schematic of CEM Vehicle-to-Vehicle Test 2 initial conditions

Key objectives for the test included the following: 

• Activation and complete operation of the PBC system: 

o Complete push-back of the CEM coupler deformation tube 

o Impact of the CEM coupler head with the sliding slug 

o Failure of the shear bolts connecting the sliding lug to the draft pocket. 

o Push-back of the sliding lug to accommodate complete push-back of the CEM 

coupler to allow the vehicle ends to engage. 

• Impact of the DAC components, with a target energy absorption of 300 ft-kips (50 

percent of its design capacity).

• Controlled motion and deformation for all impacting vehicles: 

o Engagement of colliding vehicle end structures 

o No override 

o No derailment 

o Minimal loss of occupant volume in the cab car 

5.1 Identification of Cab Car Test Vehicle

TTCI and Volpe agreed to use an M1 cab car that was onsite at TTC and available for use in 

VTVT2. Two considerations related to this vehicle affected the pre-test FE modeling effort: 

• This cab car has a buffer beam extending forward below the doorway at the end of the 

car, as pictured in Figure 54. The beam is open at the back and is connected to the end 

beam behind it, with two cylindrical spring/damper components. The FE model 

developed for the coupling tests (see Section 8.6) did not include this component, as it 

was missing. It needed to be modeled and integrated into the cab car model. 

• This cab car had not been remediated to remove asbestos. It therefore had interior 

components, including a composite floor covering. 
47 

Figure 54. Buffer beam at forward end of M1 cab car selected for VTVT2

The FE model was revised based on measurements taken from a buffer beam on a different M1 

cab car during an earlier visit to TTC and is described in Section 8.6 of this report.

It was initially determined that the asbestos should be removed only from the front vestibule 

forward, i.e., the first 3’ or so of the vehicle. Later, based on the results of preliminary FE models 

that indicated significant floor deformation further back in the cab car, it was decided that the 

entire vehicle should be remediated. A preliminary FE model had been constructed for the cab 

car based on the assumption that only the front part of the cab car floor would be removed during 

the remediation (see Section 8.6). The model was later revised to remove the floor covering that 

had been added. 

5.2 Pre-Test Finite Element Analyses

A series of pre-test FE analyses were conducted, with the primary objective of estimating a 

collision speed that would allow for meeting the key objectives of the test while minimizing the 

risk of an undesired test outcome, particularly a derailment.

Site engineers indicated they could control the collision speed to within ±2 mph. For this reason, 

the pre-test FE calculations focused on identifying a target speed range where: 

• At its minimum value (target speed minus 2 mph), the PBC system would activate and 

operate to the point where the shear bolts would fail, the sliding lug would push back, and 

the DAC would absorb 300 ft-kips of energy (50 percent of its design capacity). 

• At its maximum value (target speed plus 2 mph), the additional collision energy brought 

about by the higher speed would be accommodated in a controlled manner. 
48 

An FE model originally developed in a prior program was modified to include a second freight 

car, as shown in Figure 55. Note that the structure representing the plymetal cab car flooring was 

removed from this model in accordance with the complete removal of the flooring for asbestos

remediation. 

Figure 55. FE model for CEM locomotive impact of a consist comprising a lead M1 cab car 

with two trailing hopper cars

Preliminary analyses using this model indicated that, without the stabilization provided by 

flooring, the cab car is susceptible to buckling, particularly when the collision speed is not 

enough to cause shear bolt failure, as illustrated in Figure 56. 

Figure 56. Predicted deformation after 0.25 seconds for a collision speed of 27.5 mph 

Based on the outcome of this simulation, flooring was added back into the model, but only just 

past the forward side door opening. Subsequent results from simulations at this same collision 

speed of 27.5 mph indicate this only moved the buckle to the rear door opening, as illustrated in 

Figure 57. 

Figure 57. Predicted deformation after 0.25 seconds for a collision speed of 27.5 mph for 

model with flooring added back into the model, but only just past the forward door 

opening

Based on these results and the desire to minimize the risk of derailment, Volpe instructed the 

TTCI engineers to retrofit the entire cab car with plywood panels to mimic the original flooring. 

A total thickness of 1.0” of plywood was added; however, because panels of such thickness were 

not readily available, an overlapping series of half-inch thick plywood panels were used. These 

panels were fastened to the steel sheet floor understructure panels using screw fasteners.

The FE model was modified accordingly. In addition, the model was revised to allow for yaw 

rotation of the impacting couplers to ensure that such motion did not hinder the activation and 

complete push back of the PBC. FE results with the modified model indicated the minimum 

speed at which the shear bolts are predicted to fail is 29 mph. At this speed, a desirable outcome 

was achieved, in the sense that all the key objectives of the test were predicted to be met. A side 

view showing the predicted deformation at the end of the analysis (0.25 seconds) is shown in 

Figure 58, and indicates that localized deformation at the forward side door is minimal, and the 

cab car truck wheels do not lift off the rail. 
49 

Figure 58. Predicted results for FE model with retrofit plywood flooring and coupler yaw 

rotation during impact at 29 mph collision speed: top — a side view showing all vehicles; 

bottom — a detailed side view showing the impacting CEM locomotive and cab car

Interestingly, at 28 mph, the outcome of the test was less desirable. The deformation tube of the 

PBC was fully exhausted, but the impact of the PBC against the sliding lug was not sufficient to 

fail the shear bolts. Instead, the load through the coupler gradually began to drop. Simultaneous 

with the drop in load was the formation of a buckle in the underframe of the cab car, near the 

front side door openings (see Figure 59). This seems to have occurred because a sizable load was 

still being transmitted through the coupler as another large load built up in the DAC. These two 

loads acting in parallel became greater than the cab carbody could withstand, particularly at the 

door opening, where the strength of the carbody cross-section was weakened. At this speed, the 

forward wheel was predicted to rise, but only by a few tenths of an inch, far less than predicted 

when the flooring had been removed. 

Note that the interaction of the PBC and the sliding lug is defined in the model through the forcedisplacement behavior of a connector element. Once the full 21” of deformation tube crush is

exhausted, the load between these two components is defined to rise rapidly. However, it is 

difficult to accurately capture the dynamics of the impact of these two stiff components. It is 

quite possible that the bolts would fail even at 28 mph, particularly if the couplers remain in-line 

and do not fail.
50 

Figure 59. Predicted deformation at 28 mph collision speed: top — a side view showing all 

vehicles; bottom — a detailed side view showing the impacting CEM locomotive and cab 

car 

Because the FE model predicts an abrupt change in behavior between 28 and 29 mph, and 

because it seems prudent to provide a “cushion” that accounts for potential inaccuracies in FE 

model predictions, researchers decided to increase the minimum acceptable test speed to 31 mph 

and, accordingly, increase the target speed to 33 mph. The predicted deformation at the target 

speed is shown in Figure 60. At this speed, there was substantial deformation in both the CEM 

and the cab car end structures, and the predicted extent of energy absorption in the DAC (710 ftkips) was well above the 300 ft-kip target. 

The predicted force-crush curve at the target speed of 33 mph is shown in Figure 61. The 

estimated force associated with key contributors to the total force is also shown.

Figure 60. Predicted deformation at the target collision speed of 33 mph: Top — a side 

view showing all vehicles; bottom — a detailed side view showing the impacting CEM 

locomotive and cab car 
51 

Figure 61. Predicted force crush curve at the target speed of 33 mph and a breakdown of 

the key contributions to the total force, including the PBC, the DAC assembly, and 

deformation of colliding end structures

FE results at 35 mph (see predicted deformation in Figure 60) indicate there was substantial 

additional end structure deformation but no undesired modes of motion or deformation, such as 

buckling of the cab car underframe or lifting of truck wheels. 

Figure 62. Predicted deformation at the estimated upper limit of collision speed (35 mph):

top — a side view showing all vehicles; bottom — a detailed side view showing the 

impacting CEM locomotive and cab car 

-200

0

200

400

600

800

1000

1200

1400

1600

0 10 20 30 40 50 60

Force (Kips)

Relative Displacement (in)

DAC PBC End Structures Total
52 

6. Vehicle-to-Vehicle Test 2 Test Results

Vehicle-to-Vehicle Test 2 was conducted on November 17, 2021. The test vehicles, 

instrumentation, and camera views were inspected on November 16. Positioning of strain gages 

and displacement transducers on the underframes of the respective vehicles were verified. A 

report details the test instrumentation and provides the raw test data for this test [15]. 

6.1 Test Outcome

On the day of the test, the weather conditions were clear with low winds. Both couplers were left 

closed, and the couplers were aligned within 1” vertically. Figure 63 is a pre-test photo of the 

impact interface. The target impact speed was 33 mph, and the actual impact speed was 32.8 

mph. Figure 64 shows the impact interface after the test. The vehicles were kept in-line. There 

was no derailment of the vehicles and no override. 

Prior to the impact, the two impacting couplers were set to their “closed” position, which was 

expected to maximize the extent of PBC stroke prior to DAC engagement, thereby reducing the 

time during which collision loads acted in parallel through both components. During the test, the 

closed couplers engaged at impact and the knuckle of the cab car coupler fractured. It appeared

that the knuckle of the CEM locomotive pushed past the vertically oriented split in the cab car 

coupler knuckle and seated against the back of the coupler head, as if the couplers had been open 

prior to impact, as can be seen in Figure 65. 

The PBC then triggered properly and the PBC head began to move back into the draft pocket. 

The PBC head continued to push back as the deformation tube deformed, and the bottom DAC 

tubes impacted the M1 buffer beam. The bottom DAC tubes deformed against the shape of the 

M1 underframe, as shown in Figure 66. 
53 

Figure 63. Pre-test photo of the impact interface

Figure 64. Post-test photo of the impact interface
54 

Figure 65. View of impacting couplers from below: M1 coupler on top, CEM loco coupler 

on bottom 

Figure 66. DAC tubes after impact, before the vehicles were separated
55 

As the PBC head moved back, the coupler carrier broke away, as designed. To prevent the 

frangible coupler carrier from interfering with instrumentation wiring, both sides were tethered 

to the draft pocket side plates. However, the tethers might not have been long enough, and one 

side of the damaged coupler carrier became caught between the sliding lug and a sliding lug 

support plate, as shown in Figure 67, causing damage to the sliding lug support plates. 

At this point in the collision, the top DAC tubes impacted the end frame of the M1, causing the 

M1 collision posts to deform inward, as seen in Figure 66 and from inside the M1 in Figure 68. 

The PBC head continued to move back and the deformation tube was expanded along its entire 

stroke of 21”, as shown in Figure 69. This was confirmed by evidence of contact between the 

limit stop mounted on the sliding lug and the rear of the PBC head, as shown in Figure 70. This 

contact was designed to occur at the full stroke of the PBC.

Figure 67. The deformed coupler carrier caught between the sliding lug and a bottom plate 

of the draft pocket
56 

Figure 68. The view from inside the M1, looking at the CEM locomotive, before the vehicles 

were separated

Figure 69. The PBC deformation tube was expanded along its entire stroke of 21” 
57 

Figure 70. Damage to the limit stop mounted to the front of the sliding lug due to contact 

by the back of the PBC coupler head

Once the deformation tube had expanded along its full stroke, impact between the limit stop 

mounted on the sliding lug and the rear of the PBC head caused the shear bolts to break, and the 

sliding lug moved back into the draft pocket, as shown in Figure 71. The sliding lug pushed back 

the full extent (10”) of the pocket behind it and impacted the back plate. The front of the CEM 

locomotive continued to deform the front of the M1. The engaged vehicles continued to move 

backward on the track together, then came to a stop approximately 575’ from the impact point.
58 

Figure 71. Sliding lug position before (left) and after (right) the impact

6.2 Damage to the Equipment

After the test, the vehicles were pulled apart. Figure 72 shows the post-test impact interface of 

both vehicles. 
59 

Figure 72. Post-test impact vehicles: CEM locomotive (left), M1 cab car (right)

6.2.1 Damage to the CEM Locomotive

The upper DAC plate and tubes were barely damaged. It appeared that the collision posts of the 

cab car folded back at such a low load that the energy absorption in the upper DAC tubes was 

minimal. The lower DAC tubes were impacted and deformed considerably. The deformation was 

not uniform, as was expected, with the bottom insides of the tubes deforming considerably more 

than the upper outsides of the tube. Both sets of DAC tubes can be seen in Figure 73. Post-test 

estimates based on the measured deformation of the four corners of each of the tubes and results 

from previous dynamic impact tests of the DAC system indicate that the energy absorption of the 

DAC was approximately 300 ft-kips, thus meeting the performance target. 

After the bottom DAC tubes were removed, the support plate behind the DAC was found to have 

deformed approximately 0.375” on the right side, and slightly less than that on the left side. This 

is shown in Figure 74. 
60 

Figure 73. Upper and lower DAC tubes, post-test

Figure 74. Post-impact deformation of bottom DAC tubes support plate, left (left) and right 

(right) sides
61 

All shear bolts broke, but one (#5) did not break as cleanly as the others, as shown in Figure 75. 

This caused some damage to its draft pocket bolt hole, as shown in Figure 76. No damage was 

imparted to the corresponding bolt hole in the sliding lug. 

Figure 75. All shear bolts broke cleanly, except #5 (bottom row, second from right) 

Figure 76. Draft pocket deformed bolt hole
62 

As mentioned previously, one of the sliding lug support plates was deformed as a result of the 

coupler carrier getting caught between the sliding lug and the support plate, as shown in Figure 

77. 

Figure 77. One of the two sliding lug support plates was deformed

The front plate of the locomotive was bent backwards on both sides by several inches, as seen in 

Figure 78. Note the angled pipes that support the front plate had been removed from the forward 

end of the CEM locomotive some time before the test. (In fact, photographs indicate they had 

been removed prior to VTVT1.)
63 

Figure 78. CEM locomotive end plate deformation on left (left) and right (right) sides

6.2.2 Damage to the M1 Cab Car

As mentioned previously, the M1 coupler knuckle fractured at impact. The knuckle of the CEM 

locomotive pushed past the vertically oriented split in the cab car coupler knuckle and seated 

against the back of the coupler head as if the couplers had been open prior to impact. The 

fracture can be seen in Figure 79. 

The collision posts of the cab car folded back due to impact by the upper DAC plate, as seen in 

Figure 68. Measurements indicated that the posts intruded into the vestibule of the cab car by 

about 29”. Figure 80 shows the damage to the end frame of the M1. Both the coupler and the 

bellmouth ended up tilted upward, as seen in the photo. This was due to the M1 draft sill 

buckling. The draft sill deformed downward by about 15”, as shown in Figure 81. 
64 

Figure 79. M1 coupler knuckle fracture (left), and a close-up of the fracture (right)

Figure 80. Post-test damage to M1 end frame
65 

Figure 81. M1 draft sill before impact (top) and after impact (bottom) 

The cab car was “crippled,” with a large buckle forming in the underframe just forward of the 

rear side doors, as shown in Figure 82. The center sill of the cab car buckled downward by about 

9”, just forward of the rear door, and upward by about 6”, near the center of the rear door. Severe 

folds arose in the floor, side walls, and roof in the area of the buckle. Figure 83 shows the 

damage in the interior at the rear door buckle.
66 

Figure 82. M1 carbody buckled inboard of rear doors 

Figure 83. M1 interior damage, buckle at rear door 
67 

7. Vehicle-Vehicle Test 2 Post-Test Evaluation

7.1 Data Review and Analysis

Test data were compiled and filtered by TTCI and provided to Volpe and CAMX in an Excel 

file. A report provides the raw test data for this test [15]. Data from accelerometers, string 

potentiometers, and strain gages were reviewed relative to what they reveal about the impact 

sequence, vehicle motions, collision forces, and strain near shear bolts. Key results are 

summarized in several time-history plots and, together, provide a sense of both the magnitude 

and timing of key events during the impact. 

Note that, in contrast to VTVT1, it is difficult to determine the timing of key impact events based 

on longitudinal acceleration data. For this reason, a discussion of the impact sequence is 

presented at the end of this section, informed by an analysis of collision forces, string 

potentiometer data, and video evidence.

7.1.1 Longitudinal Vehicle and Component Motions

Inspection of the CEM locomotive and cab car underframe center longitudinal accelerometer 

data (AMUC_X and ASUC_X, respectively, as shown in Figure 84) indicates there was much 

more high-frequency content in the respective signals compared to the same pulses for VTVT1, 

making it difficult to pinpoint the timing of the sequence of key events. The signal for the lighter 

cab carbody was particularly noisy. Some of the early oscillation of the signal was likely due to 

the fracture of the cab car coupler knuckle. 

Figure 84. CEM locomotive (left) and carbody underframe (right) center longitudinal 

accelerations (‘S’ for stationary, ‘M’ for moving)

Integrating the acceleration pulses and applying an initial speed of 32.8 mph to the CEM 

locomotive yielded vehicle speed vs. time curves, as shown in Figure 85. Note that there was an 

offset between the speeds of the two vehicles that was evident at about 0.3 seconds after impact. 

Video and post-test photographic evidence clearly indicated that the vehicle ends remained

locked together following impact, so it was likely that this offset was the result of signal drift. 

-20

-10

0

10

20

30

40

50

0 0.1 0.2 0.3 0.4 0.5

Acceleration (g)

Time (sec)

ASUC_X

-10

-5

0

5

10

15

20

0 0.1 0.2 0.3 0.4 0.5

Acceleration (g)

Time (sec)

AMUC_X
68 

Figure 85. Calculated vehicle speed time-histories

Integrating the respective speed vs. time curves yielded vehicle displacement time-histories. 

Subtracting the derived displacements of the respective vehicles provided an indication of the 

relative displacement between the vehicle centers, or “crush.” The relative impacting vehicle 

displacement time-history calculated in this manner is shown in the left plot in Figure 86. This 

curve indicates the relative displacement was still increasing after 0.5 seconds — clearly not 

consistent with the noted evidence that the vehicle ends locked together shortly after impact. A 

better estimate of the displacement time-history can be obtained by subtracting what is likely 

signal drift that can be identified through the difference between the velocities of the respective 

vehicles shown in Figure 85 (known to be essentially the same since they were locked together). 

Using the average value of this difference between 0.3 seconds and 1 second (∆V=2.42 mph) and 

subtracting a displacement equal to t*∆V yields the corrected relative displacement time-history 

shown at the right in Figure 86, indicating the maximum crush was about 57”.

Figure 86. Vehicle relative displacement obtained from integration of the speed pulses 

shown in Figure 85 and subtraction of the respective vehicle displacement time-histories

(left) and correction (right) 

A better indicator of the total crush of the vehicle ends are post-test measurements made between 

different points on the colliding vehicles, as well as video evidence. Two post-test measurements 

were made while the vehicles were still on the track: the distance between the center of the front 

0

5

10

15

20

25

30

35

0.0 0.2 0.4 0.6 0.8 1.0

Speed (mph)

TIme (sec)

CEM Locomotive Cab Car

0

10

20

30

40

50

60

0 0.1 0.2 0.3 0.4 0.5

Displacement (in)

TIme (sec)

Corrected Relative Displacement

0

10

20

30

40

50

60

70

80

0 0.1 0.2 0.3 0.4 0.5

Displacement (in)

TIme (sec)

Relative Displacement (Crush)
69 

wheels of the respective forward trucks (146” right side; 148” left side — 147” average), and the 

distance between the front plate of the locomotive and the end of the side wall/side sill of the cab

car (13” right side; 15” left side — 14” average). Note that neither of these distances were 

measured prior to the test; however, FE model coordinates indicated that the undeformed 

distances were 198” and 59.6”, respectively. Subtracting the measured values from these 

presumed undeformed distances yielded the following estimates of crush: 51” and 45.6”, 

respectively. The 5.4” difference between these two measures was likely an indication that the 

end frame of the cab car pushed back a few inches.

High-speed videos provided another indication of total crush. Images shown in Figure 87 and 

Figure 88, taken from one of the high-speed videos (“East Iso.mp4”), give a clear indication of 

the extent of crush between the end structures of the CEM locomotive and the cab car. 

Figure 87 shows an image made just before impact. The image is annotated with dashed yellow 

lines, indicating distinct longitudinal reference points on each of the respective vehicles: the topfront left corner of the locomotive hood and the end of the cab car side wall/side sill, where the 

cladding becomes rounded. Dimensions taken from the FE model indicate that this distance is 

approximately 64” at impact. (The indicated distance of 64.9” takes into account about 0.6” of 

pre-impact travel at 32.8 mph over 1.045 msec). The image in Figure 88, from a high-speed test 

video taken about 280 msec after impact, clearly shows these two longitudinal reference points 

to be effectively coincident, indicating that the maximum crush was about 64”. In the figure, the 

top-front corner of the locomotive hood has been pushed all the way to the end of the side wall 

of the cab car, where the cladding begins to curve inward at the forward end of the vehicle. 

Figure 89 shows still images from the overhead standing drone video taken: (1) near the point of 

maximum crush and (2) after elastic rebound (i.e., close to a state where the post-test 

photographs were taken). These images are consistent with the model results shown in Figure 59, 

and further indicate an extent of rebound that appears to be 12” to 15” (note that the grid on the 

locomotive hood is 6” x 6”).
70 

Figure 87. Image from high-speed video annotated to indicate the distance just prior to 

impact between reference points on each vehicle.

64.9”
71 

Figure 88. Image taken from a high-speed test video (approximately 280 msec after impact) 
72 

Figure 89. Still images from the overhead standing drone taken near the point of maximum 

crush (top) and after elastic rebound (bottom)

The string potentiometer data measuring CEM coupler motion are plotted in Figure 90 and 

indicate displacements rose to about 18” after 0.070 seconds, at which point the shear bolts 

failed. It is not clear why the measured stroke was less than the 21” stroke of the PBC. It is worth 

noting, however, that these string potentiometers also underestimated the extent of PBC stroke 

during VTVT1, indicated by deformation tube markings. Also note the rise and fall of coupler 

displacement after 0.020 to 0.025 seconds that was clearly associated with initial coupler impact 

followed by the failure of the cab car coupler knuckle.

Further evidence of the timing of shear bolt failure and sliding lug sill impact with the back of 

the draft pocket can be gleaned from the string potentiometers that measure longitudinal motion 

of the sliding lug. As illustrated in Figure 91, string pot displacement began to rise after 0.070 to 

0.080 seconds and smoothly increased until 0.105 to 0.110 seconds, at which point there was a 

sharp jump in displacement, followed by a much noisier response. It is not clear from these 

curves why the displacement continued to increase beyond the 10” depth of the draft pocket, but 

it is clear from photographs that at least one of the two string potentiometers was damaged 

during the collision. 
73 

Figure 90. CEM coupler longitudinal motion, as measured by string potentiometers 

DMCL_X and DMCR_X

Figure 91. Sliding lug longitudinal motion, as measured by string potentiometers DMSL_X 

and DMSR_X

String potentiometers measuring DAC crush (see Figure 92) indicated that the crush of the lower 

DAC tubes began about 0.045 seconds after impact. Interestingly, there was a slight lengthening 

of the string just after impact, likely due to the rotation of the DAC tube end plates that occurred

due to the vertical offset of the lower DAC with respect to the buffer beam of the cab car. Highspeed video evidence (e.g., “East Wide-View.mp4”) suggests that the initial impact of the lower 

DAC tubes with the M1 spring-loaded buffer beam likely occurred between 0.019 and 0.025 

seconds after impact, but the DAC tubes did not appear to begin to deform until the springs were 

compressed and the stiffer end beam of the cab car is loaded. There was a low-magnitude signal 

from the DAC string pot that was consistent with this video evidence, and further suggests that 
74 

the energy-absorbing capacity of these springs was minimal. Note that because the cab car 

knuckle failed, allowing the couplers to move another 7” closer to one another before PBC force 

build-up, the PBC stroke was only about 6” to 8” when the DAC engaged. For this reason, there 

was a period of about 0.04 seconds during which the PBC and DAC components acted in 

parallel. Video evidence supports pre-test FE predictions (consistent with end structure 

geometric features) that impact of the upper DAC tubes with the cab car collision posts occurred

about 0.02 seconds after impact of the end beam and the lower DAC tubes. As is evident from 

post-test photographs, there was little deformation of the upper DAC tubes — perhaps 0.3” or so 

at the left tube, most of which appeared to be elastic, dropping to about 0.1” after a few seconds. 

Figure 92. DAC longitudinal motion, as measured by string potentiometers DMACR_X 

and DMACL_X (lower DAC tubes) DMACTR_X and DMACTL_X (upper DAC tubes)

7.1.2 Vertical Motions

Recall that VTVT1 test videos indicated a noticeable cyclic pitch (bouncing) of the CEM 

locomotive carbody on the suspension system of the forward truck during the collision (nearly 

±4”; see Figure 37). This was attributed to missing limit stops on the CEM truck-to-body 

connections. For VTVT2, the limit stops were in place, and the CEM pitch motions were much 

less pronounced, as indicated in Figure 93. 
75 

Figure 93. CEM forward (left) and rear (right) truck secondary suspension vertical 

displacements indicate less than 0.4” of body-to-truck relative displacement

The vertical motions of the cab car truck forward secondary suspensions were larger, as 

illustrated at left in Figure 94, but still less than about 1”. On the other hand, the relative vertical 

displacements between the rear cab car truck and body were more significant, reaching over 3” 

in magnitude, as shown at right in Figure 94. These higher displacements were likely the result 

of the high compressive force through the cab car center sill and the subsequent buckling of the 

center sill forward of the rear door. This appeared to have had the effect of raising the carbody, 

as indicated in an image taken from one of the high-speed videos (“South.mp4”) approximately 

480 msec after impact (see Figure 95). The time at which this image was captured coincided with 

the initial positive displacement peaks indicated in Figure 94. Note that the wheels of the rear 

truck are off the rail in this image. The 3–4” positive displacement at this time was consistent 

with the researchers’ understanding of how the limit stops of the cab car trucks function, 

allowing for about 4” of stroke before lifting the truck with the carbody. The subsequent negative 

displacement was likely associated with the wheels again coming in contact with the rail and 

secondary suspension compression. This was followed by continued oscillation of the 

suspension, as is visibly noticeable in other test videos. 

Further analysis of the “South.mp4” video indicated the buckle in the cab car underframe/body 

began to grow at about 140 msec after impact, peaking between 420 msec and 480 msec, and 

then decreasing. The absence of any significantly large acceleration signals during this time 

suggests that the growth of the buckle occurred at a very small longitudinal force, which was not 

surprising given the magnitude of the buckle, which appeared to be well over 18” and may have 

reached 2’ at its peak.

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0

Displacement (in)

Time (sec)

 DMLTR_Z Inch DMLTL_Z Inch

-0.4

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.0 0.5 1.0 1.5 2.0

Displacement (in)

Time (sec)

 DMTTR_Z Inch DMTTL_Z Inch
76 

Figure 94. Cab car forward and rear truck secondary suspension vertical displacements

Figure 95. Image captured from high-speed video approximately 480 msec after impact, 

showing the upward folding of the cab carbody at the induced buckle just forward of the 

rear doors, causing the rear truck wheels to lift off the rail

-0.8

-0.4

0.0

0.4

0.8

1.2

0 0.5 1 1.5 2

Displacement (in)

Time (sec)

 DSLTR_Z Inch DSLTL_Z Inch

-4.0

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

4.0

0 0.5 1 1.5 2

Displacement (in)

Time (sec)

 DSTTR_Z Inch DSTTL_Z Inch
77 

7.1.3 Collision Forces

As noted, it is difficult to estimate collision forces based on vehicle accelerations due to the 

higher-frequency content of the pulses. The impacting coupler strain gages provided a good 

indication of the force between the two vehicles up to the point that the DAC impacted the buffer 

beam of the cab car. Averaged force time-histories estimated based on strain gage data and 

assumed coupler shank cross-sectional areas are shown for the respective couplers in Figure 96. 

These curves indicate:

• A build-up in force for about 0.015 seconds followed by a drop in force and a subsequent 

increase through approximately 0.022 seconds. This was likely due to the impact and 

failure of the coupler knuckle.

• Several milliseconds during which the force was relatively uniform, at about 600 to 800 

kips. This was likely indicative of PBC push-back. 

• A drop in load at about 0.080 seconds that appeared to be when the shear bolts failed. 

One would normally expect a sharp jump in load associated with impact of the coupler 

with the sliding lug, but this did not seem to have been the case. This may have been due 

to the interference from the failed coupler carrier that acted to cushion the impact. 

• An abrupt impulse did, however, arise at about 0.105 to 0.110 seconds in the PBC only. 

Additional evidence (see below) suggested that this sharp rise in load was due to impact 

of the sliding lug with the back of the draft pocket.

Figure 96. Force through impacting couplers estimated based on strain gage data and 

known coupler shank cross-sectional area

Once the lower DAC tubes impacted the end beam of the cab car, the load between vehicles 

quickly increased. Because of the oscillations in the colliding vehicle longitudinal accelerometer 

data shown in Figure 84, it was difficult to estimate a total force-crush curve for this test. Figure 

97 shows a force-crush curve estimated from the longitudinal acceleration data. As is evident in 

this figure, even when a lower-frequency filter (CFC30) was applied to the data in lieu of the 

standard CFC60 in an effort to filter out the oscillations, it was difficult to interpret the curve.

Nonetheless, the plot does show the force rising after about 20” of crush — to as much as 1,500 

kips before falling. This was likely due to the build-up of force when the lower DAC tubes and 

then the upper DAC tubes impacted the end frame of the cab car. 

-200

0

200

400

600

800

1,000

0 0.025 0.05 0.075 0.1 0.125

Force (kips)

Time (sec)

Estimated Force through Push-Back Coupler

-200

0

200

400

600

800

1,000

0 0.025 0.05 0.075 0.1 0.125

Force(kips)

Time (sec)

Estimated Force Through Cab Car Fwd Coupler
78 

The lower load levels evident in Figure 97 between 36” and 57” are consistent with the small 

forces that are typically associated with post-buckling behavior. 

Figure 97. Colliding vehicle force-crush curve derived from CEM longitudinal acceleration 

data (Figure 84, left) and predicted relative displacement between the CEM locomotive and 

the cab car (Figure 86, right) presented for two filtering frequencies: CFC60 (standard)

and CFC30 (non-standard)

7.1.4 Strain Near Shear Bolts

Time-histories of strain aft of the eight top and bottom shear bolts on the draft pocket side plates 

are shown at the left in Figure 98. Time-histories of strain forward of the eight top and bottom 

shear bolts on the sliding lug side plates are shown at right. 

Table 3 reports averaged values (front and rear, top and bottom, and left and right sides) for the 

eight strain gages mounted to the draft pocket side plates and the eight gages mounted to the 

sliding lug slide plates. (Note that positive strain readings indicate compression.) Strain gage 

readings for the draft pocket and sliding lug bolt hole regions were reasonably consistent with 

results from VTVT1 and the 9-mph CEM coupling test [9] during which the PBC triggered. 

However, average peak strains (and, therefore, loads) for the draft pocket were higher because 

the load through the PBC increased to the point where the shear bolts failed. 

-4500

-4000

-3500

-3000

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

0 10 20 30 40 50 60

Force (kips)

Displacement (in)

CFC60 CFC30
79 

Figure 98. Left — time-histories of strain aft of the eight top and bottom shear bolts on the 

draft pocket side plates; right — time-histories of strain forward of the eight top and 

bottom shear bolts on the sliding lug side plates

Table 3. Comparison of averaged measured peak strain levels (microstrain) during vehiclevehicle tests with those from 9-mph CEM coupling test[9]; note that positive strain gage 

readings were compressive

Time-histories of strain near the top of the draft pocket sides plates (one positioned near the front 

of the side plate and one near the rear) are shown at the left in Figure 99. Time-histories of strain 

along the web of the underframe main I-beams, near where the lifting pads are positioned, are 

shown at the right. All these measured strains were relatively small, roughly 200 microstrain, 

until the sliding lug impacted the back of the draft pocket at about 0.105 seconds, at which point 

there was a large impulse applied to these strain signals. Prior to this impact, the strain levels at 

the front draft pocket side plate appeared to be compressive, while those at the back were tensile. 

The strain levels along the web of the main I-beams were mostly tensile, with the strain levels 

near the top of the web having a higher magnitude. It was difficult to draw conclusions based on 

these results, given the gradients in stress in these regions and the small magnitude of these 

strains. Nonetheless, they appeared to be consistent with FE model predictions, as discussed in 

Section 7.2. 

-200

0

200

400

600

800

1,000

1,200

1,400

0 0.05 0.1 0.15 0.2 0.25

Microstrin

Time (sec)

 SMDP1 um/m SMDP2 um/m SMDP3 um/m SMDP4 um/m

 SMDP5 um/m SMDP6 um/m SMDP7 um/m SMDP8 um/m

-400

-300

-200

-100

0

100

200

300

400

500

600

0 0.05 0.1 0.15 0.2 0.25

Microstrin

Time (sec)

 SMSL1 um/m SMSL2 um/m SMSL3 um/m SMSL4 um/m

 SMSL5 um/m SMSL6 um/m SMSL7 um/m SMSL8 um/m

Front Rear Left Right Top Bottom

9 mph Coupling Test 380 530 550 360 490 430

VTVT1 550 670 530 700 600 630

VTVT2 630 730 590 770 650 720

9 mph Coupling Test 40 -150 -40 -60 -30 -70

VTVT1 80 -130 -40 0 -20 -20

VTVT2 60 -120 0 -50 -20 -40

Draft Pocket Side Plate

Sliding Sill Side Plate
80 

Figure 99. Left — time-histories of strain near the top of the draft pocket side plates (‘1’ 

front and ‘2’ rear); right — time histories of strain along the web of the underframe main 

I-beams (‘T’ top and ‘B’ bottom) 

7.1.5 Collision Sequence

Combining evidence from the CEM coupler strain gages, the string potentiometers on the pushback coupler and the sliding lug, and images from high-speed videos suggest the collision 

sequence summarized in Table 4. 

Table 4. Estimated timing of key collision events

Timing (msec) Event

0 − 15 Build-up of force in the colliding couplers

15 Failure of the cab car coupler knuckle

15 − 22 Decrease in force as the coupler heads moved past one another

22 − 25 Secondary build-up of force in the colliding couplers

25 Activation of the push-back coupler deformation tube

45 Impact of the lower DAC tubes with the cab car end frame

60 Impact of the upper DAC tubes with the cab car collision posts

45 − 120/160 Continued crush of the lower left and right DAC tubes

80 Impact of the PBC with the sliding lug limit stop and shear bolt failure

80 − 105 Post-bolt failure motion of sliding lug

105 Impact of sliding lug with back of draft pocket

100 Buckle in cab car side body became apparent

280 Maximum extent of crush

420 Maximum extent of cab carbody buckle

480 Maximum extent of cab car rear wheel lift

680 Cab car rear wheels returned to rail

-600

-400

-200

0

200

400

600

800

0.00 0.05 0.10 0.15 0.20 0.25

Microstrain

Time (sec)

 SMCRT um/m SMCRB um/m

 SMCLT um/m SMCLB um/m

-400

-300

-200

-100

0

100

200

300

400

500

0.00 0.05 0.10 0.15 0.20 0.25

Microstrain

Time (sec)

 SMTDR1 um/m SMTDR2 um/m

 SMTDL1 um/m SMTDL2 um/m
81 

7.2 Comparison of Test Results with Pre-Test Model Predictions

Pre-test predictions of behavior during the test are compared with test results in this section. In 

general, the outcome of the test was reasonably consistent with key model predictions. With 

respect to the target speed, the researchers recognized going into the test the need to balance the 

risk of two non-ideal outcomes: one in which the collision speed was not sufficient to meet 

targets with respect to CEM component activation and energy absorption, and the other where

the damage to one of the vehicles would lead to derailment. The cab car was of particular 

concern, especially given (1) the asbestos remediation process that removed the floor and interior 

seating, both of which strengthened the car and increased its resistance to crippling; and (2) the 

age of the car, and the associated potential that its strength and stiffness had degraded over time, 

or that certain assumed properties, such as truck secondary suspension characteristics, do not 

match actual values.

The FE-based, 33-mph target speed was chosen so that, even at the low end of the expected 

speed range (31−35 mph), there was still some leeway with respect to having sufficient collision 

energy to completely exhaust the PBC and fail the shear bolts. FE model results indicated the 

bolts would fail at 29 mph, giving a 2-mph cushion. As noted above, simulations at lower speeds 

indicated non-ideal outcomes in which the cab car absorbed much of the collision energy due to 

collapse of the end frame and buckling of the draft sill and floor structures prior to the shear 

bolts’ failure. 

By and large, the key predicted test outcomes were realized, with shear bolt failure, DAC energy 

absorption of around 300 ft-kips, and no derailment and no indication of vehicle override. 

Differences between model predictions and test results can be largely attributable to three

factors:

1. The knuckle of the cab car coupler failed, allowing the CEM coupler knuckle to move 

past it and seat the coupler heads together as if they had been open at impact. This caused 

the impacting vehicles to move closer to one another by about 7”, with little or no stroke 

of the PBC deformation tube. 

2. The upper DAC tubes did not crush extensively, and, instead, the collision posts which 

they impacted folded, causing the cab car end beam to rotate back significantly. It seems 

likely that the modeled strength of the collision post was greater than its actual strength. 

This was most likely due to the lack of a strong connection between the sheet that closed 

off the C-shaped post and the flanges of the post. These two parts of the posts separated 

completely from one another at the impact point. Because the upper DAC tubes did not 

absorb much, if any, energy, there was more extensive deformation of the cab car end 

structure than anticipated.

3. The plywood flooring that was added to replace the original plymetal floor of the cab car 

came completely loose during the collision. It appeared that the screw connections 

between the plywood and the floor stiffeners were not strong enough the keep these 

structures intact. 

With these differences in mind, several comparisons between model predictions and test results 

are highlighted below.
82 

7.2.1 Vehicle Motions 

Post-test measurements indicated that the extent of crush between the CEM locomotive and the 

cab car was between 45.6” and 51”. Video evidence (see Figure 87 through Figure 89) indicated 

that the maximum penetration of the end frames was about 64”, with an extent of rebound in the 

range of 12” to 15”, yielding a crush of 49” to 52”. 

The FE model prediction of peak relative displacement at 33 mph was 54.3”. (Interpolating 

results from the 31-mph analysis indicated that, at 32.8 mph, the extent of peak relative 

displacement would be 53.7”.) This was about 10” less than the relative displacement estimated 

from the high-speed video. The predicted extent of relative displacement after 0.25 seconds was 

52.8” (and dropping), suggesting that the final displacement would likely be closer to about 51”. 

Figure 100 shows the predicted relative displacement vs. time curve compared to both the raw 

and corrected estimates of relative displacement obtained from test data by double-integrating 

the longitudinal acceleration curves measured at the respective centers of each vehicle 

underframe, and then subtracting one from the other. Interestingly, while the corrected curve 

matched the predicted final crush reasonably well, the FE model prediction was actually more 

consistent with the uncorrected curve through the first 0.16 seconds following impact. It may 

have been the case that the longitudinal acceleration response of the cab car was affected by the 

buckling of the cab car underframe/body, which began at about this time.

Figure 100. Comparison of predicted relative displacement vs. time curve with raw and 

corrected estimates obtained from test data 

0

10

20

30

40

50

60

70

80

0 0.1 0.2 0.3 0.4 0.5

Displacement (in)

Time (sec)

Estimated from Test Data (Raw)

Estimated from Test Data (Corrected)

FE Model Prediction
83 

The FE model’s under-prediction of crush by about 10” was likely due to three factors: 

1. The 7” of additional travel of the impacting couplers with little energy absorption prior to 

knuckle failure 

2. The additional cab car end frame deformation that arose because the collision posts were 

weaker than anticipated. 

3. The shortening of the cab car associated with the crippling of the carbody. 

7.2.2 Force-Displacement Curve

As noted above, the noise in the acceleration signals made it impossible to accurately estimate 

the total collision force. Moreover, the drift in the signal led to differences in vehicle velocities 

late in the test, when the CEM locomotive and cab car were locked together, making it difficult 

to accurately determine the relative displacement time-history of the colliding vehicles. At best, 

the force through the coupler could be compared, which was equal to the total force prior to the 

lower DAC tubes impacting the cab car end beam. This comparison is shown in Figure 101. The 

comparison was made more difficult by the failure of the cab car knuckle, which produced a 

large up and down spike in load between 8” and 12” of displacement and also affected the 

displacements associated with activation of the deformation tube. Nonetheless, there is some 

level of consistency between the curves.

Figure 101. Comparison of force through the CEM coupler estimated based on coupler 

shank strain gage readings (see Figure 96, left) with FE model predictions

For completeness, a comparison of the estimated total force vs. crush is shown in Figure 102. As 

is evident, and for the reasons listed above, there is little agreement between these curves. In 

addition to the oscillations present, it appears that the buckling of the cab car collision post, 

which likely occurred at about 24” of crush, completely changed the character of the subsequent 

-200

0

200

400

600

800

1,000

0 10 20 30 40

Force (kips)

Displacement (in)

Test FEA

Cab Car 

Coupler Failure
84 

force-displacement behavior, as very little force was required to produce additional end frame 

deformation. 

Figure 102. Comparison of total force vs. displacement derived from CEM longitudinal 

acceleration pulse with FE model predictions

7.2.3 Energy Absorption

Certain calculated/estimated energy absorption totals for the test and the model are compared in 

Table 5. Because reliably estimating the total force displacement curve was not possible, the total 

energy absorbed during the collision likewise cannot be accurately estimated. The PBC 

deformation tube energy absorption is assumed to be near its design value of 1,030 ft-kips. The 

estimate of DAC energy absorption was a little more difficult, particularly because the tubes did 

not compress uniformly. A rough estimate of DAC energy absorption was made based on 

measurements of DAC displacement at the four front corners of each lower DAC tube, yielding

around 300 ft-kips – the test target. This was much less than the FE-predicted value of 710 ftkips for the entire DAC assembly, and also significantly less than the predicted value of 500 ftkips for the lower DAC tubes. It was likely that most, if not all, of this difference in predicted 

DAC energy absorption is attributed to the preferential deformation of the cab car underframe 

and collision posts, which were weaker than expected and clearly not able to withstand the forces 

transmitted through the anti-climbers. Note that, based on their force-displacement 

characteristics, each of the draft gears were expected to absorb about 70 ft-kips of energy when 

compressed to the push-back load. Draft gear energy was estimated based on integrating the 

coupler force-displacement curve over the first 12” of displacement, as the force rose to the 

push-back load. Based on this calculation, it appeared that the draft gears absorbed 

approximately 280 ft-kips of energy, almost twice as much as they otherwise would have 

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

0 10 20 30 40 50 60

Force (Kips)

Relative Displacement (in)

Estimated from Test Results FE Model Prediction
85 

because they were loaded, then unloaded, as the cab car knuckle fractured, and then loaded 

again. 

Table 5. Comparison of estimated CEM component energy absorption levels from the test 

with FE model predictions

Component Test

(ft-kips)

Model

(ft-kips)

PBC Deformation Tube 1,030 1,030 

PBC/Conventional Locomotive 

Draft Gears 280 140 

DAC Lower Tube Assembly 300 500 

DAC Upper Tube Assembly 0 220 

7.2.4 Strain Near Shear Bolts

A contour plot of longitudinal strain in the draft pocket side plate during PBC pushback (see 

Figure 103) indicates the model predicted lower strain levels than were measured in the test, as 

was the case for VTVT1 (see Table 3). Strain levels were again greatest near the top-forward 

bolt hole, also contrary to test results. This is again likely the result of using connector elements 

to define the shear bolts and the associated difficulty in determining their influence on the 

stiffness of the structures surrounding the bolts. 

The contour plot shows an area of compression near the top-front of the draft pocket side plate 

and an area of tension near the rear-top of the side plate. This is consistent with the test results. 

Because there was a sharp gradient away from the peak locations, it was not surprising the 

measured magnitudes were small.
86 

Figure 103. Contours of strain on the side of the draft pocket during deformation tube 

stroke

Expanding the contour plot to include the web of the underframe main I-beam (see Figure 104), 

it appeared there were pockets of tensile strain near the location of the lifting pad, as indicated.

These pockets of tension, in the range 200 to 300 microstrain, seemed to be reasonably 

consistent with the measured values, but, because the values were small and the gradients sharp, 

it was not possible to make definitive conclusions regarding the consistency of model predictions 

and test results.

Figure 104. Contours of strain on the side of the draft pocket during deformation tube 

stroke

7.2.5 Modes of Deformation

As previously noted, key differences between the model predictions and the test results included 

the failure of the cab car knuckle, the extensive deformation of the cab car collision post with 

little deformation of the upper DAC tubes, and the crippling of the carbody near the rear door 

opening. 

Location of Lifting Pad
87 

Figure 105 shows a comparison of predicted DAC crush with a post-test photograph. The noted 

differences are apparent. However, it appeared that the mode of deformation of the lower DAC 

tubes was consistent with the test result and was indicative of impact of the end beam with the 

lower inside regions of each lower DAC tube. 

Figure 105. Comparison of FE model prediction of CEM end frame mode of deformation 

with a post-test photograph of the end frame (right)

The end frame of the cab car deformed extensively, with the collision posts folding back due to 

impact of the upper DAC tubes, which did not deform extensively, indicating the collision posts 

could not support a load sufficient to initiate DAC tube-folding. Figure 106 shows a comparison 

of the predicted cab car end crush with a photograph of the crushed end. The predicted folding 

back of the collision post and associated rotation of the end beam was consistent with the test 

result.
88 

Figure 106. Comparison of FE model prediction (left) of cab car end frame mode of 

deformation with a post-test photograph of the end frame (right)

A graphic from the FE model highlighting the undeformed distance (approximately 70”) between 

the back of the cab car collision post to a vertical post below the middle of the endmost 

passenger window is shown at the top of Figure 107. A similar graphic shown at the bottom in 

Figure 107 highlights the predicted deformed distance (approximately 42”) as well as the height 

above the rail (71”) at which the maximum intrusion occurred. These results indicate that the

predicted intrusion of the post into the vestibule of the cab car was about 28”. 

A post-test measurement indicated that the distance between these two points was 41.5” 

(compared to the 42” predicted distance). A further measurement indicated that the maximum 

intrusion occurred approximately 66” above the rail, about 5” less than the FE model predicted. 

The deformed plot in Figure 107 shows the draft sill was pushed down by the forces exerted 

upon it at the colliding interface. Post-test measurements indicated the minimum distance 

between the pushed-down draft sill and the rail was approximately 16” at a distance of 48” 

forward of the front wheel of the forward truck. The FE-predicted distance to the rail at this 

location was about 20.5”. Figure 108 shows a comparison of predicted draft sill deformation with 

a post-test photograph. The more extensive measured downward deformation of the cab car was 

likely the result of the more extensive deformation of the cab end relative to the model. The 

lower position of the fold in the collision post was consistent with this more extensive downward 

deformation. 
89 

Figure 107. A graphic from the FE model showing the deformed cab, annotated with the 

undeformed distance from the back of the collision post to the middle of the endmost 

passenger window

Figure 108. Comparison of FE model prediction (left) of cab car draft sill mode of 

deformation with a post-test photograph of the draft sill (right)
90 

7.3 Assessment of CEM Locomotive Damage/Repair Needs

The damage to the CEM vehicle was reviewed with test site personnel. The lower DAC tubes 

experienced extensive damage and will be replaced prior to the next test. As noted, the upper 

DAC tubes appeared to have deformed very little during the test, with only minor scratches 

visible, and will not be replaced. 

The PBC was of course exhausted and will be replaced, as will the shear bolts and bushings. 

Likewise, the coupler carrier was destroyed, by design, and will be replaced.

Two additional components experienced extensive deformation: 

• The sides of the end plate on either side of the draft pocket were bent backwards by 

several inches (see Figure 78). The extent of the deformation was exacerbated because 

the upward-angled tubes connecting the end plate to the underframe were missing. Test 

site personnel indicated it would be possible to bend these plates back. Note that these 

plates are not expected to be deformed during the upcoming train-to-train test. 

• One of the two “rail stopper” plates bolted to the bottom plates of the draft pocket 

assembly and support the sliding lug was bent. It appeared the coupler carrier did not fall 

out of the way as intended and became wedged between this plate and the head of the 

PBC (see Figure 77). It is possible that the retention cables that were added to prevent the 

coupler carrier from falling to the track may not have had enough slack designed into 

them. Both support plates will be replaced for the next test.

In addition, it appeared that one of the holes in the draft pocket side plate through which the 

shear bolts were positioned became ovalized (see Figure 76) due to the high loads it experienced 

prior to and during shear bolt failure. This will be repaired for the next test.

To summarize, based on the post-test inspection of the vehicle and discussion with test site 

personnel, the following replacement/repair activities were recommended:

• Replace the PBC.

• Replace the shear bolts and bushings. 

• Repair the ovalized shear bolt hole in the draft pocket side plate. 

• Replace the lower DAC assembly. 

• Replace the coupler carrier and add a few inches of cable to the coupler carrier retention 

device. 

• Replace the draft pocket sliding lug support plates. 

7.4 Lessons Learned/Recommendations for the Train-to-Train Test

In anticipation of the upcoming train-to-train test, a few lessons that can be taken from the posttest analysis of V2VT2 include: 

• If the colliding couplers are placed in their “closed” position, it is likely that the knuckle 

of one of the two impacting couplers will fail. If the post-failure behavior of the colliding 

couplers is similar to what it was for this test, the heads of the couplers will continue to 
91 

move until they are effectively coupled. This additional relative motion (about 7”) 

changes the impact sequence in that contact of the DAC will occur at a lower level of 

PBC stroke. Given the uncertainties associated with knuckle failure, it may be worth 

considering having the couplers open as they were for VTVT1. In any event, the pre-test 

FE model calculations should accommodate this likelihood.

• The lack of upper DAC deformation suggests that it may be too strong for impact with 

cab cars. It may be worth revisiting the design strength of this sub-component, 

particularly with regard to the load required to buckle the angled support plates. This will 

not likely affect the collision behavior in the upcoming train-train test, as the 

conventional locomotive end frame is much stronger than that of the cab car.

• Researchers had difficulty replicating the inherent strength/stiffness of the original cab 

car flooring with retrofit plywood. For the train-to-train test, special care should be taken 

to ensure the plywood is well-connected to the flooring substructure. Also, FE models 

should explore the consequences of having flooring that is much weaker than what it 

otherwise would be if the plywood was well-connected to the rest of the carbody. 

• The coupler carrier impeded the motion of the PBC into the draft pocket of the CEM. 

While it did not appear that this strongly affected the activation of the shear bolt failure 

process, the manner in which the coupler carrier is tethered to the front sides of the draft 

pocket, including the extent of slack in the connecting cable, should be reviewed prior to 

the train-to-train test.

• With regard to instrumentation, researchers found it difficult to estimate the collision 

force and relative displacement of the impacting vehicles. This may be made a little 

easier in the train-to-train test due to the heavier colliding vehicle weights; however, it 

will be critical to have reliable estimates of forces through all of the coupled interfaces. 

Also, alternative means of estimating displacements, such as high-speed video analysis, 

may be warranted. 

• The strain levels measured on the sliding lug were small. If additional channels are 

needed, these gages are good candidates for elimination. The same can be said of the 

draft pocket side plate gages and the underframe gages, especially given the spatial 

gradients in strain in these regions.
92 

8. Construction of Finite Element Models

The research team made a number of modifications to the FE model for analyses conducted to 

support the two vehicle-to-vehicle tests. In support of pre-test analyses conducted in support of 

V2VT1, the team made several changes to the FE model simulating the CEM locomotiveconventional locomotive collision. Each change was implemented in Abaqus/CAE [16]. Journal 

files (.jnl) documenting the interactive model development process were organized and edited so 

they could not only be used to re-create the model but also easily edited to implement 

modifications to the model.

8.1 CEM Locomotive Coupler Carrier

To increase its fidelity, the team modified the FE model of the CEM locomotive to include a 

more explicit representation of the coupler carrier. This allowed the impact between the coupler 

and the coupler carrier to be more directly modeled, as well as the failure of the coupler carrier.

The modified CEM locomotive model with the more explicit representation of the coupler carrier 

is shown in Figure 109. In the figure, the sprung top box is shown in yellow, the bottom support 

box shown in red, and the side bolt locations shown in dark blue. The detailed side view (below 

right) of the modified CEM locomotive model illustrates the contact that will occur between the 

PBC head and the coupler carrier after about 8” of push-back. 

Figure 109. Left — the front end of the modified CEM locomotive model, with the new 

representation of the coupler carrier highlighted in red; above right — the new coupler 

carrier model; below right: detailed side view of the modified CEM locomotive model

Revised Coupler Carrier 

Eight 3/8” Bolts Connecting Coupler 

Carrier to Front of Draft Pocket 

Three Vertical Springs (Each 400 lb/in) 

Supporting Coupler

Contact Between Coupler 

and Coupler Carrier 

7.75”
93 

The model for the coupler carrier featured an upper open box connected by three vertical springs 

(each with a stiffness of 400 lbf/in) to a lower open box into which it fit. The coupler rode on the 

upper open box, supported by the vertical springs, and pushed it down under its own weight. The 

sides of the lower box were connected to the extensions of the draft gear side plates with eight 

0.375”-diameter steel bolts modeled with connector elements, each with a strength of 

approximately 8,000 lbf. Contact conditions were imposed between the coupler and the frangible 

coupler carrier so that it was impacted after about 8” of push-back, then failed, moving out of the 

way of the coupler head. Welded areas that ran across the lower box connecting its side plates to 

its bottom plate were defined to have reduced strength; these were intentionally designed to be 

weak to increase the frangibility of the coupler carrier when encountering a longitudinal load. 

8.2 Conventional Locomotive Plow

Project researchers modified the FE model of the conventional locomotive to include a plow. 

Starting with an existing model for the plow developed in a previous program [17], they worked 

with engineers at the test site to incorporate measurements of key plow features from the 

locomotive to be used in V2VT1 (Locomotive 4117). The FE model of the plow is shown in 

Figure 110. 

Figure 110. Front and back views of FE model for a conventional locomotive plow 

Most of the curved plow, shown in light gray, was 0.25” thick steel. The center and lower few 

inches of the plow (dark gray and green) had doubling plates and were modeled as 0.5” thick. 

Behind the curved plow surface were vertical and horizontal gusset plates. The horizontal gusset 
94 

plates (dark blue and yellow), bolted to the end plate of the locomotive, were 1” thick. The 

horizontal stiffener plates (light blue and green) were 0.5” thick. Researchers integrated the plow 

model into the Abaqus/CAE [16] model of the conventional locomotive, as illustrated in Figure 

111. The plow extended approximately 22” in front of the end plate, as indicated. 

Figure 111. FE model of conventional locomotive with plow added

8.3 Modification of Collision Post and Other Short Hood Structures

Further revisions to the FE model of the conventional locomotive included modifications to the 

collision post and other structures inside the short hood to reflect the pre-S-580 [18] condition of 

Locomotive 4117 that would be used in V2VT1. These revisions included 0.375” collision posts 

with an angled flange and 0.125” sheets welded in front and behind that were determined based 

on measurements taken during an inspection of the inside of the short hood of Locomotive 4117. 

In addition, the thickness of the short hood was reduced to 0.125” to reflect its pre-S-580 

construction. An image of the FE model of the conventional locomotive with the short hood skin 

removed is shown in Figure 112. 

12.2”

21.9” Model Plow Dimensions were Matched to 

Measurements on Locomotive 4117
95 

Figure 112. FE model with hood removed to reveal collision post modifications

8.4 Hopper Style Freight Car

An FE model for a hopper-style freight car that would trail the cab car and be ballasted to 

equalize consist weight during VTVT2 was developed and implemented in Abaqus/CAE. The 

geometry of this generic hopper-style car was based on photographs and dimensions of hopper 

cars from several manufacturers’ web pages. For example, some dimensions were taken from 

specifications for the GBX 5200 covered hopper car [19]. Components for the car model include: 

• A stiff, box-shaped center sill

• A frame consisting of side and end top rails, side and end sills, and side and end posts. 

• Cross-bearers connecting the center sill and the side sills. 

• A tub formed from thick plates, with the bottom of the tub having a serrated shape to 

represent the internal compartments and gravity outlet gates. 

• Trucks 

• A rigid-body representation of the connected rear cab car and forward freight car 

couplers, with compliance for the respective draft gears modeled with connector 

elements.
96 

The car was assigned an empty weight of 60 kips, including 10 kips for each truck, consistent 

with specifications for the GBX 5200. Additional mass was added to bring the total weight of the 

cab car (about 90 kips) and the freight car to 232.6 kips (the weight of the CEM locomotive). 

Figure 113. Side and isometric views of FE model of hopper-style freight car

8.5 CEM Locomotive Modifications

Based on the test results for V2VT1 and subsequent evaluation of damage, several changes were 

made to the CEM locomotive model that would be used in simulations of V2VT2. Two 

modifications were made to increase the stiffness and strength of the connection between the 

angled support plates: 

• A 4”-deep by 9”-tall by 1”-thick stiffening plate was added behind the front plate where 

the DAC angled support plates were welded to the front plate, as highlighted in red at left 

in Figure 114. 

• A 0.375”-thick bearing plate was added to the front plate where the angled support plates 

were welded, doubling the thickness in this region, as highlighted in red at right in Figure 

114. 

Cutouts were made to the floor sheets in this same area; these provided access to the back side of 

the front plate and had been made when the locomotive was first retrofit. These sheets were only 

0.060”, so it was unlikely that these cutouts greatly affected the structural integrity of this region.
97 

Figure 114. Left — detail from FE model showing added stiffeners (red); right — size of 

bearing plate increased (larger rectangles highlighted in red) to include area where angled 

DAC supports were welded to front plate. 

Informed by an analysis of differences between pre-test model predictions and V2VT1 test 

results performed as described in Section 4, the DAC tubes and the angled support plate were 

extended forward by 1.125” to account for use of shell elements to model the front plates and 

bearing plates (see Section 4.2). 

An excerpt from a DAC drawing (14424-0400) [8] shows that the top DAC assembly extended

18.875” from the end plate, as illustrated in Figure 115. 

Figure 115. Excerpt from drawing 14424-0400 [8] showing that top DAC assembly 

extended 18.875” forward from the end plate of the CEM locomotive 

Added Stiffeners Behind DAC Angled Supports

& Cut Hole in Floor Plate

Increased Size of Bearing Plate to Include DAC 

Angled Support Connection to Front Plate
98 

Because the model used shell element representations of the DAC structures, the crush tubes and 

angled support plates had to be extended an appropriate distance forward from the end plate to 

permit contact with the colliding conventional locomotive end structures (note that, for contact, 

the half thickness of the bars welded to the upper DAC cross plate added another 0.25”). The 

1.125” sections at the back of the four tubes and two angle plates, shown in Figure 116, were 

assigned properties that rendered them effectively rigid, so they just transmitted forces through to 

the end plate. 

Figure 116. Detail from modified CEM locomotive model showing 1.125”-deep sections 

added to the four DAC tubes and the angled support plates

8.6 Cab Car Modifications

The FE model for the M1 cab car model was also modified. 

A composite floor cover was added from the vestibule back to the end of vehicle. The floor 

cover, comprising a 0.72”-thick plywood sheet sandwiched between a 0.14”-thick plastic top 

sheet and a 0.03”-thick aluminum underlay sheet, was not included in the original M1 cab car 

model because the vehicle used in the coupling tests had been remediated to remove asbestos. 

The original plan was for the cab car to be remediated only to the back of the front vestibule, so 

flooring was added from there to the end of the vehicle, as is shown in Figure 117. Note that, 

later, researchers decided the entire vehicle should be remediated, so the floor covering added 

here was removed for the later simulations of VTVT2. However, these simulations indicated that 

without the strength and stiffness provided by the floor cover, the cab car was susceptible to 

localized deformation of the sub-floor panels and sidewall structures, particularly near the open 

side doors. For this reason, the car was retrofitted with plywood panels (two 0.5” layers) to 

enhance the strength and stiffness of the floor. The floor structure was added back into the 

model, and the properties were modified so that they were representative of the plywood. 

18.625” 17.0”

1.125”

0.5”
99 

Figure 117. Modified cab car FE model showing added flooring, highlighted in red

In addition, an open, box-shaped buffer beam (not part of the M1 cab car used in the coupling 

tests) was added, along with spring connections to the end beam behind it, as illustrated in Figure 

118. The spring connection was modeled in a fashion similar to what has been used for the CEM 

locomotive shear bolts and the cab car coupler carrier side bolts. Small, circular rigid disks were

defined at the locations of the ends of the longitudinal springs connecting the buffer beam to the 

end beam of the car. These springs were somewhat arbitrarily defined, given the absence of 

specifications, to have a spring stiffness of 400 lbf/inch. With this small spring constant, it does 

not take much force to push the buffer beam back against the end beam. 

Figure 118. Detail showing front end of modified cab car FE model with added buffer 

beam, highlighted in red, and small round discs representing the ends of springs coupling 

the buffer beam to the end beam of the car, highlighted in yellow
100 

Finally, a connector representing the aft draft gear was added. This connector was assigned the 

same properties as the forward draft gear. It connected the rear draft pocket of the cab car with 

the rigid body representation of the coupled rear cab car/forward freight car couplers. 

8.7 New Coupler Models

In anticipation of VTVT2, one of the issues that arose was whether the couplers should be open 

or closed for the test. The couplers were open for VTVT1. This allowed for smooth push-back of 

the PBC, but, as noted in Section 4.1, decreased the extent of stroke of the PBC prior to DAC 

engagement by about 10.5”. This significantly affected the outcome of the test and, in particular, 

increased the required impact speed for full activation of the PBC to shear the bolts connecting 

the sliding lug to the draft pocket side plates. This was one of the contributing factors that 

resulted in the shear bolts not failing during the test. 

Partly for this reason, the research team decided the couplers would be closed for VTVT2. There 

is precedence for this, as the couplers appear to have been closed for both of two previous trainto-train impact tests[20][21]. Also, it is more likely that they would be closed during normal 

operation. 

There was concern, however, about whether the impact of two closed couplers might cause one 

or both of them to rotate such that the longitudinal force through them would decrease to a point 

where it would be insufficient for push-back and failure of the shear bolts. Analyses conducted 

several years ago appeared to suggest the push-back of the PBC occurs so quickly that there is 

not enough time for significant rotation; however, the documentation of these analyses has been 

lost.

To help answer this question, the VTVT2 model was modified to first add a yoke behind the cab 

car coupler and partition the PBC to allow isolation of its yoke. It was then further modified to 

treat the couplers as deformable structures connected to their respective yokes through a pin that 

allows yaw rotation and vertical motion but no pitch/roll rotation or lateral/longitudinal motion. 

The FE model for the yoke is shown in Figure 119. 

Figure 119. FE model of cab car yoke 
101 

Attempts to run simulations of VTVT2 with the modified coupler definition were not successful, 

due to runtime errors associated with poorly defined geometry (leading to poorly defined 

elements) in the respective couplers. The CAD model for the couplers was created in an earlier 

program [8] and were intended to be “looks-like” representations of the coupler rather than more 

exact geometries required for FE model creation. Prior to this recent change this had not been a 

problem, as the couplers had been modeled as rigid bodies. 

To address this issue, both couplers were recreated in Abaqus/CAE, using the geometry of the 

existing couplers as a guide. The respective couplers are pictured in Figure 120. The cab car 

coupler was 28” long (longitudinal distance between coupler pin and knuckle pin, as indicated) 

and the CEM locomotive coupler was 31” long. The couplers were defined to have identical head 

geometries, differing only in the length of the shank and the presence of a feature on the 

underside of the longer CEM locomotive coupler to impact the frangible coupler carrier. 

The FE model for simulation of VTVT2 were updated to incorporate these new coupler models. 

Figure 120. FE model of new cab car (28”, left) and CEM locomotive (31”, right) couplers 

28” 31”
102 

9. Conclusion

Two full-scale, vehicle-to-vehicle tests have been conducted that evaluated a CEM system 

retrofit onto a conventional passenger locomotive to enhance its crashworthiness. Pre-test 

activities in support of V2VT1 indicated a target speed of 21 mph ± 1 mph would meet test 

objectives of a complete PBC stroke with shear bolt failure and energy absorption in the DAC of 

at least 50 percent of the design specification, with some margin for error. The actual test speed 

was only 19.3 mph, well below the minimum expected speed. The various components 

performed as designed: the vehicles remained in-line with no derailment and no signs of 

override, the stroke of the PBC deformation tube appeared to have been exhausted, and the DAC 

energy absorption levels met test targets. However, due to the low test speed, there was not 

enough energy to fail the PBC shear bolts. Two FE model-related factors were identified as also

contributing to the lack of shear bolt failure:

• The test was conducted with the couplers open. This effectively increased the closing 

distance between the vehicles prior to load build-up in the PBC and effectively reduced 

the extent of PBC deformation prior to DAC engagement, which altered the load path 

and caused significantly more energy absorption prior to PBC shear bolt failure. 

• The DAC bearing plate and front plate were modeled as shells. This effectively reduced 

the extent to which they extended forward from the end plate of the locomotive, which 

also increased the extent of energy absorption prior to PBC shear bolt failure. 

A post-test assessment of damage revealed one issue regarding the design of the CEM 

locomotive support structure that needed to be addressed prior to V2VT2. Welds at the 

connection of the DAC angled support plates to the end plate of the CEM locomotive were 

damaged. FE model results showed localized plastic deformation in this area. A repair was 

implemented in which a gusset plate was added behind the end plate, and a bearing plate was 

added in front of the end plate. Longer term, it is likely that increasing the size of the collision 

post flange/DAC bearing plate to include the region where the angled support plate is welded 

will be sufficient to alleviate this issue.

A post-test review of test data indicated that strain gages mounted to the surface of the coupler 

shank provided an excellent estimate of forces through the coupler and were generally better than 

accelerometers mounted near the center of the CEM locomotive carbody for determining force 

build-up during PBC deformation prior to engagement of the DAC. Post-test model simulations 

for relative vehicle displacement, vehicle speed, force-vs.-crush behavior, and mode of 

deformation compared quite favorably to test results.

Pre-test FE modeling in support of VTVT2 indicated a target speed of 33 mph ± 2mph would 

meet test objectives of complete PBC stroke with shear bolt failure and energy absorption in the 

DAC of at least 50 percent of the design specification, with some margin for error. These models 

further indicated that the collision forces that arise in this test might challenge the buckling 

resistance of the cab car, particularly because the original flooring was removed. Interestingly, 

these models indicated that this mode of deformation was less desirable at speeds where the 

shear bolts did not fail, leading to buckling of the carbody/underframe near the forward side 

doors of the cab car.
103 

V2VT2 collision speed was 32.8 mph – very close to the target. The test was successful, with all 

key test objectives met, including exhaustion of the PBC deformation tube stroke and failure of 

the shear bolts. The colliding vehicles did not derail, nor did one override another. However, the 

cab car was “crippled,” with a large buckle forming in the underframe just forward of the rear 

side doors. This caused the wheels of the rear truck to lift off the rail, and it was fortunate that 

they fell back onto the rail without causing a derailment.

The knuckle of the cab car coupler fractured just after impact. It appeared that the knuckle of the 

CEM locomotive pushed past the vertically oriented split in the cab car coupler knuckle and 

seated against the back of the coupler head as if the couplers had been open prior to impact. This 

changed the deformation mode, with the DAC loaded much earlier with respect to the stroke of 

the PBC. In addition, it appeared that the coupler carrier did not fall away fast enough and 

became trapped between the push-back coupler head and the support plates for the sliding sill. 

Despite these two unexpected events, the PBC performed as designed, suggesting that it has 

some robustness with respect to deformation modes at the collision interface that might differ to 

some extent from those of the idealized design. 

The FE model captured certain aspects of the collision well, but there were some key differences 

in deformation mode, particularly because the upper DAC plate and tubes were barely damaged

in the test. Instead, the cab car collision posts folded back at a lower load than expected, and the 

energy absorption in the upper DAC tubes was minimal. Revisiting the design of the upper DAC 

assembly may be warranted. Nonetheless, the predicted cab car end frame deformation was quite 

similar to that observed in the test. 

The post-test review of test data again indicated that the strain gages mounted to the surface of 

the coupler shanks provided an excellent estimate of forces through the coupler and were 

generally better than accelerometers mounted near the center of the CEM locomotive carbody for 

determining force build-up during PBC deformation prior to engagement of the DAC. The data 

from string potentiometers were also very useful in determining the timing and magnitude of key 

component behavior.

Overall, the vehicle-to-vehicle impact tests were very successful. The primary objective to 

demonstrate the effectiveness of the components of the CEM system working together to absorb 

impact energy and to prevent override in two different vehicle-to-vehicle collision scenarios was 

met. The FE analyses predicted the behavior of the equipment in both collision scenarios with 

high fidelity. These results give researchers a high degree of confidence in the modeling and test 

preparation for the last test in the program, the train-to-train test. 
104 

10. References

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Modifications for Locomotive and Cab Car Anticlimbing Systems [DOT/FRA/ORD-03/05]. 

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Energy Management Passenger Rail Equipment: Structural Results. American Society of 

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[9] Llana, P., Jacobsen, K., Stringfellow, R. (2019). Conventional and Crash Energy 

Management Locomotive Coupling Tests [DOT/FRA/ORD-19/36]. Washington, DC: U.S. 

Department of Transportation, Federal Railroad Administration. 

[10] Rakoczy, P., Gorhum, T. (2019). Conventional Coupling Test Between Coach Car and 

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105 

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106 

Abbreviations and Acronyms

ACRONYMS EXPLANATION

ASME American Society of Mechanical Engineers

CEM Crash Energy Management

CG Center of Gravity

DAC Deformable Anti-Climber

FE Finite Element

FRA Federal Railroad Administration

TIP Test Implementation Plan

TTC Transportation Technology Center

TTCI Transportation Technology Center, Inc.

PBC Push-Back Coupler

V2VT1 Vehicle-to-Vehicle Test 1

V2VT2 Vehicle-to-Vehicle Test 2